Computer powers up, no display, just repaired graphics card

Jan 28, 2019
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I have a Sapphire Radeon R9 280 in my computer. It was getting on a bit and the fans were failing. I bought a replacement fan set, took the card out, replaced the fans, put it back in. It all seemed pretty simple.

When I turn the computer on now, it powers up seemingly normally, lights come on, fans spin including on the graphics card, but the monitors don't detect anything. EDIT: There's no power to the keyboard or mouse, may not be POSTing?

I've tried different monitors, monitors running from the motherboard, reinserting, turning off and on etc.

I'm low to average on the skill dept so it's possible I've made some rookie error.

Any thoughts or guidance?

I don't have exact details on my PC (can't boot) but it's from about 4 years ago, decent at the time, I5 or I7, newish 750W power supply, working fine before my fan replacement operation.