My 4-5 year old Alienware laptop got to the 'Alienware' start up screen yesterday but failed to boot. It shows the scrolling circle beneath Alienware, then screen goes black, keyboard lights go off, I hear the hard disk cut out and it tries to restart. And so on forever.

This morning I managed to get it to restart and log on so I quickly backed up everything. Tried a restart and it seemed fine but a few hours later and it's stuck in the boot loop again.

FYI: It has frozen a few times while sitting idle lately. But never while in use, even when gaming. And it had a replacement battery fitted around two years ago by Dell.

Can anyone suggest a potential cause and first step? Thanks in advance.