hey what was your previous graphics card? It might be drivers conflicting with your new card.
Remove your card & try to turn on your pc. Let me know if it still causes problem?
I would suggest remove all the cabinet connectors from motherboard like power button, reset button etc. Turn on your pc directly from motherboard with the help of screw driver. Problem might be in your power button if pc starts up normally.
what gpu are you trying to buy? Every pci-e 2.0 or 3.0 is backward compatible on your 1.0 motherboard.
If you looking at high end gpu, u might have to change your whole system as ur performance will be halted by cpu and to some extent by your motherboard's pci-e slot.
Yes you can. But your old motherboard drivers may conflict. I would suggest just re-installing windows to get your pc fully properly functioning and avoid further problems.
if you are using windows 10 then open task manager> go to processes tab and check if there is service(like service host) or any other app using anything in Network column.