Low CPU usage - Application(s) not responding

I built a system in early June using an AMD Athlon X2 (4850e) on a MSI MB (K9A2 Platinum) with 4GB of DDR2 1066 RAM and dual HIS 3850 graphics cards; the OS is Vista 64 SP1. Everything has worked fine for the past 4 months, but a couple of days ago I began experiencing applications locking up, from 10-15 seconds to more than a minute; most often this is with Outlook 2007 and Firefox 3.0.3. When this happens memory is about 1/4 used and the CPU drops to 3% or less. The application will put a 'not responding' message in the window header and get a translucent overlay; and even though the applications(s) are not responding they are also not consuming any CPU cycles according to Task Manager. There have been no significant changes to the system (Firefox update from 3.0.2 to 3.0.3 is all I can think of).

After the second day of this behavior I reformatted the boot drive, reinstalled the OS, drivers, applications, etc. I'd no sooner finished the rebuild and the same problem began reoccurring. I'm now suspecting a hardware problem, but would expect it to be consistent and not intermittent like it is. At this point I'm open to any ideas of suggestions.

I apologize for the cross posts in multiple forums, but this is such an odd problem I wasn't even sure which forum was appropriate.


Steve