First thing I did was doing a windows XP repair from my XP CD I got from DELL.
Then it got stuck in the repairation and I asked peoples in IRC on how to fix that, and they said to me to use CHKDSK in recovery console to repair errors on my harddisk. I did that and it found errors and it repaired them for me.
Then I tried Windows XP repair again with the XP CD, but now it won't detect my installation and ask to install a fresh copy on which partition.
Then I tried to boot to windows normally, but it couldn't because it missed files in "c:\windows\system32\config\system" I think.