Question : Problem: Computer locks for 5-10 secs about once every two minutes

I have an HP pavilion XT963 with 512Mg of Ram running Windows XP.   I have replaced the RAM, run UBCD tests on the processor, RAM and hard drive, no issues.   The computer seems to lock the mouse and keyboard about 5-10 secs about every 2 mins.   I have used new keyboard and Mouse and changed locations, buildings just to see if it is electrical.  Any ideas what would cause this?

Answer : Problem: Computer locks for 5-10 secs about once every two minutes

Sound like something is spiking the cpu usage every few minutes.

try
Process Explorer or What's Running to see if anything is doing that

Process Explorer  
http://technet.microsoft.com/en-us/sysinternals/bb896653.aspx
http://www.download.com/Process-Explorer/3000-2094_4-10223605.html

What's Running
http://www.whatsrunning.net/whatsrunning/main.aspx