You could try resetting the BIOS in case you may have unknowingly set an option at some point that may have messed with the GPU slot or locked the motherboard out of using it.
I'm thinking its an amperage or wattage issue from the PSU. What do you think?
Aye the PC can boot into BIOS and goes into windows. The VGA also does works.
Tried It and still nothing. only getting output from MOBO onboard VGA.
Additional note: Tried plugging a different GPU into the MOBO and it also produce the same problem.
Do you have another PSU you can try to use with this system? Since the graphics card works in another system I doubt the card is the issue. The PSU worked in another system, but did it work with the same requirements as the last system regarding wattage and amperage?
TLDR; we have narrowed it down to most likely being 1 of 3 components. Its either the PSU, motherboard, or the CPU.
I have explained the PSU already. It could be the motherboard having a variety of issues but those are not easy to track down. I usually try to exclude everything that is not the motherboard to implicate it as the issue.
It could also be the CPU as it has not been tested in another system and because you have not been able to get into BIOS until recently. Check the CPU temperatures in BIOS and report back if you can.
After, I would clear cMOS which can be done a number of ways. I would check your motherboard manual if you have it for exact directions. If you cannot find it power done the system and disconnect the PSU or flip its switch to off. Then take out the cMOS battery on the motherboard and hold the case power button down for 30 seconds in a row.
Let us know how that goes.