Laptop keeps rebooting after dell blue bar goes up

Hello its been months since I have used this laptop and tried EVERYTHING TO FIX IT. It starts up you see the dell logo then once the blue bar goes complete threw it turns off and restarts again. I started one night when my battery went dead and it just shut off. Next day I brought a new battery and it came on[without the power cord which I had to use since my battery was dead and would not work unless I had the cord in it] now its in a constant reboot, I have searched online for weeks,months and hours for every possible solution and many different sites but nothing, called dell and they gave me useless info and basic steps I already tried.

HERE IS WHAT I HAVE TRIED ALREADY so please don't post the same thing

-Taking the battery out and holding the power button down then putting back in

-Did the diagnostics which it passed and said everything was fine and no errors

-Cannot access safe mode only buttons that work are f2 and f12. That is it, also tried fn, windows button, shift, and etc, but none of them work.

-Just had this laptop get a brand new hard drive and motherboard from dell so that is not the issue

-Went into BIOS and reset everything to original, it did not work, I even tried the change SATA operations etc on it but did not work

-I do not have a dell windows reinstall dics since it did not come with one and I DO NOT WANT TO ERASE ALL MY FILES on my laptop/hardrive

-Tried plugging all my usb ports with usb cords then started it but I noticed it went really slower this time booting up, but issue continued.

-I even brought a brand new battery from dell which worked since my old batter ran out and died

-Tried booting from the hardrive,network,cd, etc etc but nothing

-What in the world is wrong with my laptop? I even hear once people buy or reinstall windows it continues