Be very suprised if dropping a screw on the motherboard killed your PC (I would have killed nearly a hundred by now)
Check mains lead, plug connections, fuse, switch on rear of PSU.
Connections to motherboard (you may have disturbed something)
remove card and see if it boots. May be the extra load on the PSU, has damaged the PSU. Changing (trying another) PSU would be fisrt thing after above checks.