computer really slow

[Tu]

I just got a new compaq presario with a 2400+AMD (2.0GHZ)
with 256 MB ram and it runs really fast. I put on
internet and forgot about my internet security program.
within about two days my computer is running almost 6
times slower then it did when I got it. I think I got an
attack but It's not a virus because i scaned and nothing
showed up.

What should I do?

I NEED HELP NOW

 

[Jupiter Jones [MVP]]

Install or enable a firewall IMMEDIATELY:
http://support.microsoft.com/?kbid=283673

Run an updated virus scan.
Or Scan for Viruses online:
http://security.symantec.com/ssc/home.asp?j=1&langid=ie&venid=sym&plfid=23&pkj=IRLFIZTYMWPAZTJWUFJ
Run Disk Cleanup checking all boxes except "Compress old files"
Start/All Programs/Accessories/System Tools/Disk Clean-up
Run Defrag.
Start/All Programs/Accessories/System Tools/Disk Defragmenter
If you have file sharing software such as Kazaa, disable it.
Check this link:
http://www.aumha.org/a/noads.php
Run Ad-Aware (free version) or Spybot to check for spyware:
http://www.lavasoft.de/ (Update if you already have it)
Or
http://spybot.eon.net.au/ (Update if you already have it)

This may apply if you recently installed Windows XP Service Pack 1:
http://support.microsoft.com/?kbid=815411