Please help, laptop crashing after 5 mins. Saying install operating sy

Hi all, sorry if this is in the wrong place. I'm very worried here, my work laptop has just started playing up.
I have a 64 bit machine running Windows 7. I was online earlier and the laptop crashed, once it restarted it said I had to install an operating system. I then pressed "exit" and a bitlocker error came up saying it had detected changes to the boot menu. I performed a hard reset and restarted the machine and everything seemed ok although running a bit slow. However after another 5 mins or so the exact same thing happened again. During this time Internet Explorer crashed a good few times, I think the error was to do with a exe file called something like btpr.32 this may be irrelevant but I thought I'd mention it. Any help at all would be very very much appreciated