Laptop won't start

I was facing some problem with my old windows, whenever I used some internet browser (chrome) or vlc player my laptop would get extremely slow, even moving the mouse over the screen would take time. I was facing other virus issues as well, so i reinstalled my os, in the newer os also (windows 7 ultimate, which service pack i don't know) i started facing the same problem after an hour or two. Then a few days back my computer started to shut down giving me some blue screen and a error message on it 0x00003b or 2c i don't remember now, and suddenly the last night it went off and when I turned it back on it asked me to go for start up repair, but that didn't work and then i tried for lkgc, repair but nothing worked. And now my system won't even start. It stops at the very first screen (of dell inspiron) no matter what i press f8 or f12. And sometimes it won't even do that jjust a black screen. The last time before my system went off completely it popped me up that windows defender and my anti virus was turned off (which i didn't do). PLease help me with it, i can't risk my data.