What operating system and service pack is this? The reason I ask is that as Blaster has been around since at least 2003 a fully patched system should be immune to it.
Follow the required reading here: http://community.mcafee.com/docs/DOC-1294
If that doesn't help then download, install, update (very important) and run the FREE version of THIS software and let it remove everything it finds. Reboot if asked to after the scan.
Note: all of the previous line's instructions can be achieved in "Safe Mode with Networking" if for some reason the malware prevents normal mode functions. You can reach that by tapping F8 repeatedly while booting up and selecting that option from the menu that presents itself.
(Usually item #2 on that menu).