That's a shame about your computer, Malte.

But there may still be a chance to save it. If you do not have any webcam or anyway for someone to help you remotely, another option that may help is to burn a rescue CD such as Kaspersky or AVG and run it. I recommend, if the other options don't work, to look online whenever you can and find a rescue CD and obtain one.
But if all else fails, try to see if you can get your files backed up (not sure how much this will cost) and reinstall your operating system, wipe it clean. If you don't know how to do this, there should be instructions online on how to do it, or someone here can tell you how.
Another option is to get a new OS, a free one. There's a lot of them out there you can easily option, such as the various types of Linux, Solaris, and OpenBSD. But I'd only recommend this option if you are unable to get Windows back at all on that computer and if you are unable to afford a new computer.