Sorry to hear about the mice them little ____. It sounds like they really did a number on your PC. Up to you if you think it's worth it - You could try a different GPU card.  Too bad you don't happen to have another one laying around.  If it didn't work, it would point more toward the MB needing replacement.  Even if something doesn't look burnt, who know how hot some of the components got. With the T1500 going back to 2010, who knows, you might consider something newer; all depending on your budget. T1500 MB's aren't too cheap, but could less than the cost of a newer Precision.  Be sure to get at least a 30-day return policy if you go that route.  [URL] 
The power supply works fine, tried the paper clip test. there's no mobo light, button cords seem fine. there have been mice into it recently, had to clean that. its been off for a few days bc of a power outage, which right as the power shut off, I shut off the surge cord before it got the chance to turn on again, or surge. I never got the time to game simce it went off, so I never bothered to turn it back on. so whats the issue? the mobo looks fine to me. any tests? The fan on the very back (not power supply fan) wiggles a little when I press the button sometimes. The light is solid green, and the rear usb ports still charge my devices
Precision T1500 not powering on when button is pressed