@Cyclic: That's true, System Mechanic made restore a point and backup of the registry before optimizing. On Iolo's site, they also give a guide how to find these backups and restore them. Its actually the same method as explained on this forum. I tried it but alas, to no avail.
@Britton30: It's indeed a harsh way to learn but I think my computer needed a refresh anyway. This way, not all effort is lost ^^
I think I will keep my hands of registry optimizers. I also read on this forum that windows7 has its own built-in registry cleaner using CMD, I'll probably use that in the future. Thanks though