It might be anything. Bios updates are usually released for these type of hdd /memory/cpu/graphic card incompatibities. I've checked Dell's support site and there are 9 "criticaly recommended" updates, from A6 (6/29/2010) to A15 (7/24/2011). Just update the last one and if you still have problems, at least you know you've tried it. Did you have these boot problems from the beginning? Or they started lately?