I went through a bad computer phase for a while, and honestly it's horrible. I found that you pretty much have to give up on taking the game seriously because you're going to die more than you would expect for yourself. Get a really good fps config and try to play with bare minimum settings, but if that doesn't work, just start playing the game differently. Focus on positioning and getting yourself into better situations (kind of hard for mge/dm I realize) and try playing classes that don't require super high fps (medic, heavy, engineer, etc.) since those classes are either easier to aim with or focus more on positioning/timing.
TL;DR: RELAX, TAKE YOUR TIME