liquorice, try booting into safe mode.
while the computer is booting up, hit the f8 key and select safe mode start up.
system restore is in the all programs -accessories-system tools folder.
as was suggested by others, you must make sure you have a robust firewall and anti virus installed, as system restore won't help you if a virus is the cause of your problem.
back any music, photos or important documents that you dont want
lose as soon as you can.
PENTIUM 4 3.06 GHZ WITH HT TECHNOLOGY