Hi @dell16148
Here's the [https://dl.dell.com/manuals/all-products/esuprt_desktop/esuprt_optiplex_desktop/optiplex-360_service%20manual_en-us.pdf|service manual] for the PC that may help.
Check what the light pattern of the 4 diagnostic lights on the back of the PC is and then go to p.128 of the service manual to see what the light pattern means and what you can try to do to fix the problem.