I noticed that the files causing my computer to run a consistency test (scandisk/chkdsk) everytime i restart were old .CHK files. I couldn't even run a defragmentation.
But i searched for the files, erased them, and problem solved

No more scandisk at restart, and defragmentation runs ok.
It seems kind of weird that scandisk/chkdsk had a problem with .CHK files, which are actually created when you run that sort of test.