PC always shuts down after about 1/2 hour running XP

[Rzep]

Hi,
Weird things are happening to me this morning! I have
just formatted my PC and re installed XP. After about 1/2
hour there is an error message warning me to close all
open programs as windows is about to shut down! Something
Authority comes up!
Anyone able help??

 

[me]

Virus???

 

[The Unknown]

Virus!
It appears your computer has been infected with the Blaster virus. For more
information and how to fix this please see follow this link:

http://www.microsoft.com/security/incident/blast.asp
http://www.microsoft.com/security/protect/main.asp

More information about this particular worm:
http://securityresponse.symantec.com/avcenter/venc/data/w32.blaster.worm.html

Removal Information can be found here
http://www.kellys-korner-xp.com/xp_qr.htm#rpc