Hmmm... if I didn't know any better, I'd say your computer is infected with our old friend the Blaster worm. But it's been years since I've heard of an infection.
I have been hearing some talk of this problem after updating to XP Service Pack 3. It's either a bug with SP3 or a new malware which resembles Blaster.
First, I'd recommend running a full malware scan in Safe Mode (How do I get into Safe Mode?
If the scan doesn't turn up anything and/or the Remote Procedure Call service is still dying, here's how to prevent it from shutting down your PC:
and type in services.msc
and press enter.
Scroll down to Remote Procedure Call
, right click and select properties
Go to the Recovery tab and change the settings from Restart the computer
torestart the service
This should cure the symptom, if not the cause.