Welcome to TSF.
I don't see anything suspicious here. Do a ctrl+alt+del and look under the Processes tab. Sort it by Mem Usage and see which one is guzzling all the resources when your CPU spikes to 100%.
Just to be sure there's not a virus working here, perform an online scan with Internet Explorer at Panda ActiveScan
http://www.pandasoftware.com/products/activescan.htm
* Click on 'Scan your PC' button. There should be a popup - if you have a pop-up blocker, make sure it's not blocking it.
* Click 'Check Now' & a pop-up window will appear.
* Enter your Country, State and E-mail Address & click 'Scan Now' - begin downloading Panda's ActiveX controls (8 MB size).
* Begin the scan by selecting My Computer.
* If it finds any malware, it will offer you a report. Ignore any entry it finds (since it wants you to buy the program for removal) as we will address this later.
* Click on see report. Then click Save report.
* Please post that log in your next reply.