Optiplex ram problems

Hello,

I have some Ram problems.

First I tried upgrading my Optiplex 755 with two sticks of 1gb  Kingmax DDR2-800 RAM in slots 3,4 because I wanted to reinstall Windows Vista with more RAM. That failed. Computer wouldnt boot up.

Then i took out Kingmax RAM and computer still wouldnt boot. There was only amber light power button with 1,2,3 diagnostic lights and blinking coursor after post. Also it wouldnt go to BIOS settings.

Installed new power supply and amber light wanished and also 1,2,3 diagnostic lights.

It would boot into windows and I can enter BIOS only with 1gb ram stick in slot 3. I get an alert that i have unsupported memory configuration and needed to populate Dimm 1. 

If I populate 1gb stick in slot 1 (Dimm1) I get blinking cursor on black background after post.

I ran diagnostic tools and everything seems ok.

Do I have bad Dimm1 slot? Thoughts?

Thanks,

Goran