welcome to MS Blaster virus
http://www.grisoft.com/ - AVG antivirus its free.
http://housecall.antivirus.com/ free online scan to get it quickly (assuming you can download ok)
When the message comes up go to Start --> run
and type 'shutdown /a' to ABORT the shutdown process
if you're on WinXP do start --> run --> type 'msconfig' go to STARTUP tab and UNCHECK MSBlast
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