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#11
He means remove the GPU and re-seat it in the slot. Oh and you are overdue for a complete clean and while you remove the GPU take a clean dry paint brush and brush out the slot and the rest of the computer while having a vacuum near to draw the dust away.
Also what size is your PSU? I would get some compressed air and really go to town on the PSU and system while unplugged, then re-seat the GPU and plug all back in. Dust is a electrical conductor and not good for air circulation or heat dissipation.
Did that.
Did you try cleaning the slots?? Do that with a strip of old credit card (about half inch wide with the corners rounded off) with some lint free cloth around the end of it very lightly moistened with an alcohol like denatured spirit (not much) and GENTLY wipe along the slot.
The crud that settles in the slots can get pushed down tight and prevent proper contact with the contacts on the RAM or GPU. I didn't notice if it was mentioned but "reseat" the cables to everything.
Everything appears to be alright now. Thank you all for your help.