Same problem, different history -
system AMD4 1Ghz with XP Home locking at seemingly random times.
While installing updates and patches, it crashed and entered a state of continuous reboot. After reinstalling operating system and PC Cillin, I downloaded the recommended patches and updates and updated virus library files and discovered MSBLAST.A (msblast.exe) MSBLAST.E (mslaugh.exe) and nachi.a (Dllhost.exe). These files were quarantined and then deleted. (Note: remember to deselect autorecovery).
After the cleanup, I downloaded and ran the Trend Micro Damage Cleanup a pop-up appeared that detected worm_blast.e. However, I ran a manual scan and found no viruses!?.
Subsequently, my system began periodically freezing when svchost.exe begins using 100% cpu. It happened several times when I tried to launch Explorer, although it appears to be triggered by the dial-up. After reading the posts above, I unchecked firewall, but this had no effect.
I set the RPC in Services to "Take No Action" and this appears to have solved the problem, although it is difficult to know due to the randomness of its occurrence.
Question: What if anything have I disabled by setting RPC to "Take No Action?"