Hello.  My Optiplex GX620 has pixelation issues so bad it cannot be used.  I've tried resetting the monitor, replacing the hard drive, and also replaced the VGA(?) cord.  Used to be I'd have pixelation only when the VGA cord wasn't in tightly enough, but nothing has helped correct the current problem. 

Guessing there's an issue with the motherboard but thought I'd ask for suggestions before I dump this old girl. 

Thanks.