Wireless connects and I get an IP, but I can't ping anything

Question

Alright so I installed Arch on an ION330HT, to find the wireless won't connect. I've run Arch on it before and it worked perfectly so I'm unsure what's going wrong. I have the exact same net-auto-wireless config file that I have on my other machines, so I'm sure it's not a problem with the configuration. I've tried doing it manually as per the instructions on the wiki, to no avail. I've checked the logs, and the machine receives an IP address, so I know it sees the network in some way.
The only thing I've noticed, is that the output of iwconfig has the line "Encryption key:off" in it, where as other machines don't - I'm thinking this is the issue, but I can't imagine what could cause this.
Any help would be great.

Answer 1

Alright, update. I left it pinging the router before I left home this morning, and I've just checked - out of 40,000 packets sent, 75% were lost. So traffic WAS getting through - so much so that doing pacman -Sy actually worked, although it was very slow. I recently bought a new router, that was much better than my old router, the key difference between the two being that the new one has wireless n support, where as the old one was b/g only. It was set to g/n only, so I switched it over to b/g only - it's connecting to the stage that I can ping outside addresses immediately now, however it's very slow - I get about 25 KB/s. I'm letting it crawl along at the moment, downloading 62mb of updates - maybe an update will solve this issue.
/dev/zero wrote:
What's in your "/etc/resolve.conf"? What kind of wifi card is it and have you stfwed for whether that card requires any non-standard setup?
/etc/resolv.conf (strangely, I don't have /etc/resolve.conf, but /etc/resolv.conf. My other machines are like this also):
$ cat resolv.conf
# Generated by dhcpcd from wlan0
# /etc/resolv.conf.head can replace this line
domain home.gateway
nameserver 192.168.1.254
# /etc/resolv.conf.tail can replace this line
The wifi card is an AR9285 (Atheros), no mention of any non-standard setup that I could find. There was some talk about wifi being slow for one user on the Ubuntu forums - they were advised to ditch wifi and use ethernet instead.
sftw = "Search the frickin web"
So if I ask whether you sftwed something, that means: did you do some independent research first?
So, the card worked in the past, but maybe this time you've forgotten to load or configure a module that you previously used. Or maybe a kernel update introduced a new bug? I would at least search the web to see whether things have changed in the Linux world, and maybe jog my memory in case I forgot something. There's no excuse for not stfwing before starting a new thread.
Yeah I did, I've found talk about an issue that seems very close to mine - http://forum.xbmc.org/showthread.php?t=63642 however no solution was ever reached. They came to the same conclusions that I mentioned earlier - connecting in b/g mode instead of n mode works, but is still very slow.
ip route output:
$ cat iproute.txt
default via 192.168.1.254 dev wlan0 metric 303
192.168.1.0/24 dev wlan0 proto kernel scope link src 192.168.1.4 metric 303
In addition to /dev/zero's request for the output of ip route, can you ping 192.168.1.4?  If not, can you ping localhost?  As a sanity check, are you sure your router is not at 192.168.1.1 ?
I can ping both 192.168.1.4 and localhost just fine. The router is definitely not 192.168.1.1, I've connected to it at 192.168.1.254 to change wireless settings today. Not going crazy yet