SP2 Errors and Problems

My computer is quite messed up as I downloaded and installed SP2 for Windows
XP.

Firts of all I noticed that the SP2 have been downloaded for twice and the
older SP2 installation failed somehow. The problem was called 800736CC. (but
the new one was installed normally). These are the problems that I have
noticed

When I shutdown the computer it doesn't advance to the point when the
computer should shutdown automaticly on the contrary it restarts the computer
again with an error.

The computer seems to run critical errors more than usually after installing
the SP2... (and I had it for two days now). Problems with the MSN 6.2
Messenger also. Seems to be connected but I can't talk to anyone and nobody
can talk to me (even that im on-line. Noticed this problem after I phoned to
my older bother and we both were connected to Messenger program.)

I thought also that it could be a virus but after scanning the computer
twice I didn't find any sign of 'em.

So what should I do? Should I uninstall SP2? Get new download of SP2? Or
should I re-install whole Windows XP?

Thanks for help

Kari (Finland)