Virus

If you have an antivirus program, it must be updated constantly. If it's not, you can still get infected with new variants of old viruses or totally new, designer viruses.

Free scanners:

• ClamWin Free Antivirus
• AVG Anti-Virus Free
• McAfee AVERT Stinger - only finds viruses of major outbreaks

Spyware

Some spyware digs itself so deep into your operating system that it can cause troubles beyond just annoying advertisements.

Free scanners:

• Ad-Aware SE:
• SpyBot Search and Destroy
• Bazooka Adware and Spyware Scanner
• AVG Anti-Spyware Free for Windows
• Windows Defender

CPU fan

If it's a laptop, it should have a fan to cool the CPU. Check to make sure it is periodically blowing the hot (and damaging) air out of your laptop.

Hard drive scanning

The hard drive could go bad for multiple various reasons, not limited to dropping a laptop. Using either method, lots of errors = time to get a new hard drive. Back up as many files as you can, while you still can. Both will check your hard drive for errors.

chkdsk: the nerdy, command line way

Start >> Run >> enter cmd in the Open box and click OK >> type chkdsk c: /R

It's OK to restart, but make sure you watch the output to see if there are lots of errors.

Checking the graphical way

To check the hard drive, right click on it, choose properties, click the tools tab, click the "Check now..." button, select to scan for bad sectors (and optionally fix errors), and start. It may ask to reboot. If it does, watch the screen when it does to see if it spews a long list of disk errors on the screen.