Compaq Presario C500 keyboard problems

A little history of the laptop: I bought the laptop used from a friends and All the keys work except "O", "L" and the period. I bought a brand new replacement keyboard and those buttons worked fine, for awhile. I finally bought a new Wwindows Vista cd and installed it on the laptop, since it was supposed to have Vista and it had XP for whatever reason. Still nothing, when I unplug the keyboard ribbon and plug it back in, the keys work for a while and then stop. Any answers are greatly appreciated.
Michael

Probably a defective or worn motherboard keyboard connector...

Which means nothing I can do, unless I replace the entire motherboard. Unless you know of something else?

thanks for the reply

Yes... Laptop keyboards are rather easy to replace

I've already replaced the keyboard with a brand new and the problem still persists, when you said motherboard/keyboard connector. I thought you were talking about the intergrated clip on the motherboard in which the ribbon from the keyboard fits into or what?

thanks for your reply and help.

Yes, the keyboard connector on the motherboard may be defective or worn

Can I just replace the connector or would I need to replace the whole motherboard?

Thanks again for your help

Whole motherboard....

Somehow I knew that was going to be the answer, it's never easy.
thanks again for your help