system restore in win xp

I have a second hard drive installed for backup. The second hard drive was filled and I got a low disk space warning. I have since found out that Win xp wiped out restore points to save disk space. (This doesn't make much sense since the restore points are on the primary drive wich has plenty of free space) I now have problems that I would like to fix with system restore but restore points previous to the low disk space warning have been deleted.