type cmd at run.
winipcfg -release
winipcfg -renew
that should fix it. you get a lease on a IP address. for some reason someone else connect to your network they got a lease for the same IP address. If you only have one computer connect to your router. Block by MAC address. it's a very basic way to keep other poeple off your network with out slowing your wireless down using the encryption keys. Using encryption like WEP can slow your wireless connection down. your average person doesn't know how to clone your MAC address. Most people look for unprotected wireless. there are so many out there. Why waste time cracking it, when 2 houses down is a open wireless network.

another thing people fail to say. If you profile gets corupted you computer can run slow. you don't want your XP profile to get bigger then 3 gigs. Don't store thing in your profile unless you have too. Very large profiles can cause alot of problems. create a temp or another folder in the root. Best yet have at lease 2 partitions. store your music, files, photos and other stuff on 2nd partition.
create a new profile and copy favorite and desktop to new profile. then copy my documents to the new folder on the root. Wait a day or two before you delete the old profile. it's under my computer advance tab.

setup a VM in linux to run windows. When VM windows crashs just restart it. I use Vista more then I do linux. Vista runs linux VM when I need it.

boot in safe mode with networking. create a new profile. copy from old profile to new profile. copy document, favorite and desktop folders. once you get it all copied delte the old profile. type msconfig in run. remove all the start programs you don't need or use. download spybot from download.com. spybot usually gets it all. if it still doesn't work. make a Barts disk. Boot from the CD. Run the spybot from the boot disk. There is a Linux boot CD. That's for more advance users. you would have to know how to mount and locate the drives, if there don't get mount at boot. klamav clamav is the linux virus scan. first one is the visually and clamav is the command prompt.