You may need to enable a firewall first. If XP, go to www.microsoft.com/security and click on the Sasser / LSASS virus link for
instructions. If not XP, you can still look there for instructions. www.kerio.com, www.sygate.com and www.zonealarm.com are all free firewalls,
but you might not be able to download them if a virus is hitting your
computer and making it reboot.
Check your Windows System Event log [if Windows 2000 or XP] for error
messages that might confirm whether this is an attack using LSASS or RPC /
DCOM or Messenger vulnerabilities, for example.