I think I can explain one of your problems. When you powered off the arduino but still had power to the mosfets, you don't have pull-down resistors wired between the mosfets gate and source terminals (10k ohms is good) the arduino output pins 'floated open' when the arduino powered off so there wasn't an electrical 0vdc on the gates to turn the mosfet's off. I Also don't see a gound wire from the laptop PS nigitive to an arduino ground pin, but you must have done that or it wouldn't have worked in the first place. Add the resistors and that shouldn't happen again.
About the Uno not working I can't say but sounds like you blew the chip somehow. Time for a replacement 328P chip with uno bootloader preloaded.