Computer Freezing/Monitor flickering

I hope I am in the correct forum.
I have a PIII that has been in my closet for a while that my son wants to hook up to his computer. It worked when I put it in there but now the monitor flickers and when I click on any icon it freezes. Replaced the memory and tryed another Hard Drive but it still flickers and freezes when I click anything. Have any ideas.

By the way I accidently broke one memory clip putting in the memory. I have looked every where for a clip and cannot find one. Have any ideas?
Thank you
Sheila

 

Check if the cables are properly connected. Checking the video card is also recommended.
You may want to check this article.
Five tips to fix a screen flicker

 

I would say also to check or replace or add a new video card.Also try another monitor first.

 

your looking at gpu issues or stability issues due to power supply unit. start with gpu first can pick up a cheap pci or agp graphics card for around £5

 

Thank you. I did check the cables and they are all secure including the AGP graphics card.

 

Thanks Bobby. I did have an extra PCI card that I put in my other computer to make sure it work and it did. I them put it into my son's computer and went into the BIOS and it was already set for PCI. With the PCI card and BIOS set to PCI I got nothing on my monitor and I never heard the one beep you usually heard when you first turn on the computer. I have the AGP back in the computer with the BIOS settings for PCI, which dosent make since, but the computer does come on and freezes at the Windows XP welcome screen.