I don't know why.  It just started acting funny.

Your PC may not be "acting".  It may be the real thing.  A virus.  Is your PC running noticably and consistently slower?  Does it lock up (freeze) on a regular basis?  If you have adeqaute disk space and RAM this could be a sign a virus may have infected your PC.  And there are other signs too numerous to mention.  Virus scanning software with the lastest updates are your best defense against such malicious attacks.

Recommended Virus software:
McAfee - Features real-time updates, and firewall capabilities.  Overall preferred.  There may be issues maintaining "Active" scanning at bootup.
Symantec - Otherwise known as Norton Anti-Virus.  Good user interface.  On-screen monitoring could be annoying.
Trend - very good real time update notification, small anomoly with some email servers.
F-secure - For network, file encryption, PDA and home/small business solutions.

Your Anti-Virus software is loaded and you're protected!  Really?  Confirm that background scanning is ON for Internet and Email accesses.  Just because you loaded new software doesn't mean it's doing it's job while you're not looking.

Virus Hoax Lookup:
McAfee - Also try their quick lookup system.
Symantec - for the quick lookup or do your own virus name search.
Trend PC-cillin - also very good information updates.
F-secure - also very good information updates.

Spy Ware:
There is a new demon on the horizon.  Actually the demon is in your backyard.  Actually it's in your home and it lurks about collecting information, personal information about you and your family. It's called spyware and it comes in the guise of a program, a cookie, a file in your Microsoft OS PC.  Don't be fooled in thinking a cable modem router, firewall and virus software protects your PC from intruders gathering information about your web surfing habits.

SpyHunter - with a free system scan download.
SpyBot - Search & Destroy with a list of download programs.