COMPUTER RESTARTS RUNNING WINDOWS MEDIA CENTER 2005

Hello,
I have a computer running Windows Media Center 2005 that restarts just about every day. It happens whether or not I'm running the Media Center application itself, but it seems to happen more frequently if I am running it. The Media Center interface often becomes sluggish or unresponsive, though it continues to work in a way (for example, I can be watching TV then try to go to the Guide or Recorded TV function where it will either a)just stay playing the TV program or b)go to the other menu with the TV progam in the lower corner but not switch back to full screen mode). I also ocasionally link my laptop to my Media Center by either FireWire or a direct ethernet connection to transfer large files, which also generally causes the system to restart. When this happens I get the following error displayed

''This system is shutting down. Please save all work in progress and log off. Any unsaved changes will be lost. This shutdown was initiated by NT Authority\system.

Windows must now restart because Remote Procedure Call (RPC) Service terminated unexpectedly.''

This has happened numerous times - often with another error message came up that mentioned something about ''generic host process'' and ''windows32''. I know this is known to be a blaster virus issue, but I've scanned for viruses (I have Norton 2005 running), ran the blaster fix just in case, and reinstalled the OS in hopes of eliminating the problem, all to no avail.

At this point I'm not sure if it's a hardware or software problem and was hoping to get some direction, and even more hopefully an easy or known fix, before I start seriously digging into it tomorrow.

Thanks to everyone in advance for all your help, I really appreciate it.

My current configuration is:

Asus KN8 motherboard (I originally had a bad one and replaced it)
AMD 3000+ CPU
1GB (2x 512MB) RAM
200 GB SATA HDD
2x Hauppauge 150MCE PVR cards (TV Tuners)
eVGA NVIDIA FX5700 LE 256MB Video Card (again, first one went bad and was replaced)
Linksys WRG54 wirelss card
Pioneer? DVD-RW

I got most of the components at a Microsoft roadshow for the launch of Media Center 2005, if anyone has any experience with this particular configuration.
I also have a PCI firewire card and a 8-in-1 card reader, but th problems occured before I added these, and they didn't require any drivers, so I suspect they're not part of the problem.