Can't provide you with a Danish guide. But I can point you at one good article if you are running XP as the version of Windows there. It would be helpful knowing which version is installed there.
For XP however besides using the system restore feature if that fails the repair install option is available. How to Perform a Windows XP Repair Install
The steps are easy to follow since you would simply boot with the installation disk as if you were installing a fresh copy of Windows. But instead of seeing a full install there you look to see if the option for repair of an existing copy is then seen after pressing the enter key to install Windows now.
What this does is repair install all essentials while leaving your files, folder, and even programs intact. In some cases you may have to reinstall video or sound drivers while the remaining things are left intact and ready for use.