Time Capsule Not Recognized by PC

Question

I've replaced my old router with a new Time Capsule (TC).  The router is connected to a Motorola SB6120 cable modem for internet access via my cable TV company.  Set up of the TC seemed to go smoothly, the network still has the same SSID and WEP security code as it did before, picked up automagically from the old router during the set up.  My wireless devices are a Macbook Pro (that I used to do the setup), an iMac, an iPad2, two iPhone4s (plural iPhones, not to be confused with the new iPhone4S), an HP Photosmart Premium All-in-One printer, and the problem - a Dell Inspiron N5010 PC running Windows 7 Home Premium SP1.
After completing the set up I had to re-enter the WEP security code on each Apple device and the printer when they first tried to connect to the network, even though the code had not changed, but other than that one-time minor inconvenience they all connect fine.*
The problem is with the Dell PC.  It can 'see' the network - the SSID shows in the list of available networks - and it sees excellent signal strength, but it connects with only "Limited Access".  Neither disconnecting from the network and reconnecting, nor disabling and re-enabling the network card, changes that.  Initially, running the Network Troubleshooting routine produced the following result:
- The 1st (and only) stopping point was a request to confirm the WEP security code.  The code shown was correct, but I re-entered it and continued.
- The troubleshooting routine then went through a series of other checks without stopping for user input or confirmation.
- The troubleshooting routine ended by showing 2 Problems Found:
1) the security code confirmation
2) 'IP problem' (not the exact wording, but something about an IP address problem).
After doing some research on the internet, I downloaded and installed Airport Utility on the Dell PC and tried to run it.  On launching Airport Utility I got this message on the screen, "Unable to find any Airport wireless device".
Again I tried to run the Windows Network Troubleshooting routine.  Again the 1st item is to confirm the WEP security code after which the routine runs to completion without stopping.  Now there are 2 different problems found:
1) Problem with wireless adapter of access point - Detected - triangle with ! inside
2) Windows cannot connect to [SSID network name] - Fixed - circle with checkmark inside
Any suggestions for what might be going on?  What hardware or settings I ought to check and report back on?
Thanks in advance for and suggestions anyone can offer.
* Aside: my iMac shows that the network security type is WPA2, not WEP, but it connects just fine anyway!

Answer 1

Thanks again for your suggestions and instructions, now wish me luck!
Yes, I do!!
Never mind - Google is my friend!
Sure is.
2. how do I determine which of the two networks to use?
Easy.. pick the best one. ie best signal strength and speed. 5ghz is better speed and poor range. 2.4ghz the opposite. At any point pick the best. Best signal / speed. Close to the router, it will be 5ghz.. further away 2.4ghz will be better. Try both.. it is a 10sec effort.
The reason to do this manually is the TC is designed to swap channels automatically when there is interference.. It is also so the client on the computer (mac only) will auto swap between 2.4ghz and 5ghz for whichever is faster. So you have auto channels on top of auto band.. and even the Mac gets confused .. the PC has no idea.
3. What channel should I set for the 5 ghz network?  (If I recall correctly, the TC is presently using channel 6 - does that apply to both networks?)
No.. 2.4ghz uses channels 1-11 in USA.. 1-13 in Europe Australia..
There are 3 non-overlapping channels, 1, 6, 11.. pick one and try it. Better still on the PC download the application inssider.. and you will see which channels are in use.. usually all of them if you live in a city in USA or moderately weathly country. Pick the channel with the lowest signal and use that. Since only those three channels are non-overlapping picking channel 9 for instance because nobody is using it, is pointless. Wireless on both channel 6 and channel 11 will then interfere with it. Use the lowest signal channel, out of the three, 1, 6, 11. (13 in Europe 14 in Japan).
5ghz has a large range of channels, beginning from 36 up to 151 (at least in Australia) .. your country if different will vary. Use the lower channels if possible.. but there is not much interference yet on 5ghz. Usually you can just use 40 which meets lower end equipment. eg early versions of the AEBS and TC do not offer a large range of channels.
4. Can I leave the security as WEP until I get everything working?  I understand that WPA2 is better
WEP is equal to a strong door on a tent.. it is next to useless. It keeps out people who are not trying to get in. And offers 1min of difficulty to the guy with the knife. Use no security to do setup.. then use WPA2.. if something doesn't work with wpa2 you can use wpa at a pinch. Throw away any item not compliant with at least WPA. WEP is not a rated security for N wireless.. it could well not work or fall back to G wireless. So for testing just turn off security.. when it is working jump straight to wpa2.
5. Why turn on the Guest account?  I don't see that it's used in the subsequent steps.
If you ever want to write to or read the hard disk from PC.. you will have issues with security on Windows not matching the TC.. You do not need to use guest account (this is hard disk access not wireless btw).. if you never want to use hard disk. I added it for completeness. You can also fight your way through the difference in security between a Mac and a PC with win7 in particular.. loads of fun. If the disk is going to be on a private network and the TC has to be really, then use guest network. If anyone wants to break in it is no more difficult than holding down the reset for 1sec and it will reset all the passwords. So what more security do you need. Guest is fine.
6. Will do.  I do have a workgroup specified on the 3 computers, but it's one that I created and it's not named <WORKGROUP>
SMB uses workgroup name.. what name you use is irrelevant.. again this is for hard disk access. If you just want internet it is not necessary to worry about. Put into the workgroup name the name of YOUR workgroup. But it makes it appear in the windows networking as a network drive and that can be helpful.
Somewhere on the Dell PC I've seen that both ipv6 and ipv4 show as not used, don't recall where I saw it though, and there did not appear to be any way to change it.
You have internet connection it MUST use TCP/IP which has to be either ipv4 or ipv6 or both. That is how the internet works.. you cannot have neither. You change the settings in TCP/IP properties box associated with the wireless card.. go to device manager and the wireless device. Click on it and go to properties.. see TCP/IP and go the advanced.
You need to learn to use the networking tools. 
The key tool is ping.. that allows you to see if a device is available and responding on the network.
Command window is same as terminal on the Mac.. (well near enough). You do low level commands.. both will do ping.
You can also get all the settings in the network.
Simple one is ipconfig in windows.. ifconfig in the mac.. that will show the IP address of all the network clients. In windows there is a full description if you do ipconfig /all
These commands are very important to use and learn about.