PSU died, PC fried. Need advice.

Couple days ago, i got an error message on startup(bios screen) telling me the floppy drive wasn't detected. After skipping the message, everything worked fine so I ignored it. Next day, my keyboard/mouse plugged into the USB port stopped working, so I plugged them into a different USB port, which worked, and kept going. Today, my computer crashes and won't turn back on. I could tell it was the PSU, so I unplugged everything except the video card and hard drive, turned it on, and I got to the bios screen, but couldn't get past the floppy drive error.

So, I went out and bought a new PSU hoping the rest of the system was fine, plugged it in and now everything turns on, all the fans are spinning, HDD activity light is on, all the optical drives are working. But I get no picture on the monitor. Also, the USB ports still fail to work. When I plug in my keyboard to the USB ports, the light on the receiver flickers, then turns off. When I plug it into the PS/2, the light stays on. This makes me think the mobo is fried.

So, what I'm wondering is how many components got fried? Is it possible the GPU, CPU, and/or HDD got messed up as well, and if so how can I tell, short of replacing everything, one by one?

Oh and another noob question, if my HDD/GPU are fried, and I take it over to a friends computer and plug it in to see if it works, can it cause any damage to their computer?