I noticed a thing where if I put my keyboard and mouse in different USB port things controlled by different USB controllers and only the mouse always stopped working when it did so I tried it with another mouse and now it feels like the USB problems never happened. Ill have to keep testing though just to 100% make sure that that was the thing causing the USB problems.You can try cleaning the pc and reseating all connectors, cards, RAM, and jumpers.
Which should be done on a regular basis anyway....
If possible borrow another known working PSU - 600 watts at least.
Install and then test by working as normal. If problems continue check the error codes for any changes.