Dell OptiPlex GX520 Amber Light 123 Code No POST

Monkeypie8

Commendable
Dec 31, 2016
19
0
1,520
After dusting the heatsink on the GX520 I plugged it in and amber light on motherboard. When I turn it on the 4 numbers on the front panel flash and then goes to 123 which means error on screen but there is no output.

Please help.