Windows XP Pro temporary freezing

After trying to look through some old posts, I haven't found one that really fits my situation. I am running a 1.5 GHz P4 machine with 256MB RAM, a 60GB hard disk, and an Intel M-Board. The problem is that my computer temporarily (and periodically) freezes for approximately 10 seconds every minute or two (very irritating). When it comes back, everything is fine, though. This happens the vast majority of the time I use my computer, but it strangely tends to start happening when I leave the computer idle for a few minutes. At first, I thought it was a software problem, so I reformatted both of my partitions, reinstalled XP Pro (a legit version and everything), and yet it still happens even though that is the only thing on the hard drive. I have not upgraded to any new video cards or anything and strangely enough the machine worked without this problem for about 6 or 8 months. I did buy it custom-made, however. Someone suggested I test if it happens in safe mode, which it does. At this point--with my limited knowledge--I am thinking it is a hardware problem, but I have no idea which part and would like to have a real good idea before I go and buy replacements. I ran some online utilities such as PC Pit Stop and Fresh Diagnose, but nothing seemed to be in bad shape from what I could tell. Does anyone have any ideas, please??

check you running progrmas for something using alot of system resources, sounds like a auto updater, or a program running in the background. might also want to turn off hard disk hiberation, disable system standby,the turn off hard disk feature, and the turn off monitor feature, maybe a standby issue from how it sounds.