Hm, I guess I'll just have to try again. I'll tell you if I've managed to open it. I'm not sure yet when I'll try it, though (but probably soon)... I don't really like to separate it from electricity, because whenever I plug it in and then switch the power-switch on the backside to "on", one of the cutout-switches for my apartment will trigger a couple times. I usually solve it by turning it on again and again with the power-switch of the PC being "On", until it doesn't trigger anymore xD. No idea why that happens. It's not like the PC sucks electricity just from plugging it in... I thought. Whatever. I ain't no expert; but that's why I don't like to plug my PC off... which I probably should do before I try to open the case. ^^
Edit: Thanks for the help. I think I've already tried it with that clamp back then; but I might not have tried hard enough.