Reset as in reinstall? This depends upon your machine. If your pc came with
a set of recovery discs you can use these to completely reinstall your
system. The system will then be just as you purchased it from the shop,
less, of course, the wear and tear you subjected the machine to in the
meantime. If you don't have recovery disc you may have a hidden partition on
your machine that holds the operating system files etc. Check your pc manual
for recovery options. If, on the other hand, you have a retail copy of
windows xp then you can reinstall from that cd - obviously, though, if your
pc came with other software installed you should have the cd's for that
also.