Inspiron gaming laptop stuck in boot loop

As the title says, my laptop is continuously rebooting when I turn it on. I've tried pressing F12 when it starts up, and that does bring up the diagnostic screen, but it nonetheless reboots at the same time interval even with the menu opened. Just to see what the issue might be, we unplugged the battery and used adapter power only to see if the battery was the issue, but the problem persisted. We also unplugged the hard drive, which we assumed was the issue, but even then it rebooted. My friends believe the motherboard is the issue by elimination, but i wouldn't mind other input. If it is the motherboard, could I send it into Dell and see if they could do anything? It's almost 3 years old, so I'm assuming the warranty is probably up, if theyd even do anything.

Thanks!