Go the reg key, right click...
permissions>advanced>owner>other users or groups>advanced>find now>everyone
close all property pages, then open permissions again, and add yourself in, giving full permissions. Now there are permutations to this, you might have to remove certain users etc. You have to do the above to each and every sub key if you want access to the root key, starting with the inner most nested key.
Hope I got that right, if not the sequence is close to what I posted, good luck.
BTW, make sure you set a system restore point (or some other registry backup method) before you mess with they keys.