My computer doesn't let me boot?

I try to log in but then it pops up saying system recovery but the system recovery doesn't find/do anything and keeps restarting on me. When i try to press F12 or F8 which ever one is for my Dell laptop, it doesn't give me an option to go in safe mode. I have tried to run several test on it when i click on advance settings for the system recovery but doesn't say anything is wrong. What do i do to fix it? I tried to restore it to an older time but that still doesn't work and i have tried all the restore dates too.