Lightroom is very slow, utilizes 100% CPU, then freezes or closes program. How do I fix it?

Question

I am having a problem with Lightroom 5 being very slow, utilizing 100% CPU, then freezing or closing the program.  How do I fix it?
I just upgraded to LR5 from LR3 on Sunday as well as CS6 from CS5 (which I have not tried out yet).  I spent several hours talking with Vamil, from LR Support Staff yesterday.  He was extremely helpful and kind and tried everything he could think of while remote-handling my PC and talking with me on the phone.  He deleted preferences, cache, temp files, updated graphics with a new replacement file from AMD site, then re-downloaded and reinstalled LR5. 
It is still very slow and then freezes and closes down with a message of utilizing 100% CPU.  Within several seconds of using the brush in Develop, I started having lots of problems.  I could not even move the picture around.  The side screens would not disappear like they should.  And I could not move to another picture.  The day before I spent several hours trying to work on just 1 picture.  After all the changes yesterday, I tried to move from picture number 1 to about 130 after having not touched it for 10 minutes, and a half hour later, it still said, "Processing" with no picture coming up, just a blank prieview pane.
LR Support suggested I get a new CPU though he thought according to specs mine should be ok and other programs were running fine.
My PC is only 2 years old.
I talked to HP briefly about CPU updates for my HP PC.  He said I probably do not have a problem but suggested I run self-diagnostics and maybe buy a new CPU anyway. 
I ran diagnostics listed through the HP Support Assistant connection on my PC.  All was ok. 
I still researched if I could buy a compatible CPU upgrade.  I cannot even find any CPUs still selling that are listed for my PC.  Best Buy Store said they could not even order a compatible CPU.  They said my Bus speed may not be big enough, so they suggest I get a new PC.  What Bus speed do I need?
I have the following PC Setup:
     AMD Phenom II X6 1045T Processor 2.70 GHz with 6 Cores
          with 2700 MHz Base, 3200 MHz Boost, and 4000 System Bus Speed, and 95 watts;
     HP Pavilion Elite, HPE-500y, 900 GB Free, new in 2011;
     Windows 7, 64 Bit;
     RAM 16 GB, DDR3;
     Graphics AMD Radeon HD 6450;
     Nikon, D200, with Raw Files;
     External Hard Drive for Original Photos, 600 GB Free;
     LR Catalog and Library are on Main Hard Drive;
     Monitor, Sony CPD-200ES, new in 2004.
I am thinking of buying a new monitor tonight mostly so I can do better photo work while enlarging the pictures to do it.  I am concerned that while it will help my viewing, it will take more power away, and make my usage of LR5 even worse.  Will a new monitor affect my performance?  I am looking at HP Monitors with IPS.  Is this the best recommended choice for LR and Photoshop CS6?
I think I would like to stay with a 6 core processor since I need to have several items open for other non-Photoshop functions.  When running LR5, I had everything else closed.  With LR3, I was able to have other things open.
I do not really want to buy a new computer and know that those I have talked with at this point are only guessing after looking for what they thought should fix it.  4 People from Lightroom Support have all thought I should not be having problems with my setup. 
I bought one of the best computers 2 years ago.  Is it really obsolete already so that I cannot use LR5?  Is everyone else buying a new PC every 2 years?  I used to go 5-7 years. 
Even though I have figured out some of what my PC has, I really do not know technically what I am talking about so am at the mercy of other's help.  Are there any solutions that might work short of buying a new computer?
I also have taken 40th anniversary photos for some people and am waiting to give them as a free gift since I am not a professional at all.  I am hoping to get through this problem soon so that I can provide some nice memories for them.
I have not gotten any further than trying to adjust 1 picture.  I have no comments on uploading speed, since I did that while still in LR3.
Thank you for your time and help.

Answer 1

I'm running LR with no speed issues on an Intel 17-860 quad core with about the same performance as your AMD Phenom II X6 1045T Processor. My system is also an HP, which originally had a single 1TB 7200 HDD. I've since added a second 2TB Black Caviar HDD, which provided no significant difference in LR's performance.
AMD processors do not implement hyper-threading and don't need it. I'd start debug by process of elimination:
1) Disconnect all externally attached USB, FireWire, or other externally connected devices except keyboard, mouse, and your single 1280 x1024 display. This includes all externally attached memory card readers, phones, ipads, etc.
2) Reboot and logon as Administrator.
3) Remove your Internet connection and turn off all Antivirus and firewall programs.
4) Open LR and under Catalog Settings set 'Standard Preview Size' to 1440 (slightly larger than your display width). Under the Metadata tab here make sure 'Automatically Write changes into XMP is NOT checked.
4) Create a 'New Catalog,' Create a new folder and add about 10 raw image file copies to it for testing, and Import it into the new catalog. In the Import module make sure under File Handling 'Render Previews' has 1:1 selected. Wait until all Preview building has completed in the Library module.
Try editing these image files inside the new catalog as you were previously.