League of Legends client used to run fine, now won't open on my computer

Hey...

I don't know how to troubleshoot for this or what to say, the thread title says it all, I guess. Anytime trying to open LoL, just results in error reporting window. Up until maybe 1 week ago, the game seemed to run fine, but now no.

Not to mention I have trouble with a lot of other software too. I can still use Audacity, OpenMPT, Renoise; but GoogleChrome, Steam, nor League of Legends won't work anymore. Maybe someone stole certain internal parts from my machine, replaced them with cheaper parts, and now it doesn't meet the required technical specifications anymore? Unlikely, but it's just a theory.

Anyone have an idea for how to fix this? :D