My monitor will frequently freeze, go black then start working again. Other times, everything just freezes.
This used to happen often before, then I noticed that my power bar (very old) had a flickering power indicator... I replaced the power bar with a new one and the problem went away until recently. (possibly not related... )
Let me know what I need to tell you... I have run CCleaner numerous times as well as AVG anti-spyware and I currently have running Symantec Anti-Virus (2005).

thanks in advance for your effort! you people are great!

The monitor going black could be one problem and the system freezing another. Or both could be related.

We need to know more about your system. I am assuming this is a PC and not a laptop? How old? When the monitor goes black, how long until it comes back. That could be the monitor or the video card, or the PSU. The easiest way to eliminate the monitor from the equation is to swap monitors with another computer.

Do you have a separate video card or is it built in? Have you cleaned the insides of the computer of heat trapping dust and dirt?

When the computer freezes, how do you get it going again?

What version of windows?

It is a PC.
Bought it brand new almost 2 years ago.
Monitor freezes for 5-10 seconds, goes black for about 5 seconds, then comes back.
I will try swapping monitors after this post.
Separate video card (Radeon 9250).
Will clean the inside of the 'puter after this post (though I have done this before).
When it freezes, I just restart it (hit the reset button on the tower) or press and hold the power button to turn it off.
Windows XP Home Ed. 2002 SP2
Next?

It sounds like the video card right now - will see what happens when you swap monitors. If the problem moves with the monitor, then obviously the problem is with the monitor. But if it happens with the second monitor, then all that tells us is it is something in the PC. Could be video card, could be RAM, or a failing motherboard.

It is not good that you have to kill the power - that is not good on hard drives as data can be corrupted. You should back up any critical data as soon as you can.

When inside cleaning, inspect the motherboard for leaky capacitors. They look like tall soda cans, with many surrounding the CPU socket. Look for white to dark brown, dried foam leaking out the tops or bottoms. Bulging caps are a sign it is about to leak. Also make sure all the fans spin freely.

To test your RAM, I recommend MemTest86+. Select Download - Pre-Compiled package for Floppy (DOS - Win). Unzip the file to a convenient location, insert a formatted floppy disk in the floppy drive, double-click on install.bat to install. Then, with the floppy in the drive, reboot the computer. The computer should boot to the floppy and start testing your RAM. Let it run for several passes or even overnight. You should have no reported errors. Instructions to create a bootable CD version is available too. An excellent how-to guide is available here.