Computer shuts down

Today, after picking up my Dell Inspiron 1470 from the technical support (to replace the speakers), I was told that the motherboard had been replaced too.

When i got home, and turned it on, it began to freeze (100% cpu usage) and shut down randomly, and the task bar icons weren't shown properly.

I restored windows 7 to a previous state and it began to work fine, except that after 15 minutes it began to shut down again. And when i tried to boot it it kept shutting down even before than the last time.

I ran Dell Diagnostics tool and in the process of checking the computer, it also shuts down. So i'm assuming it has something to do with the new motherboard rather than being a software/malware/virus problem.

I just emailed Dell technical support letting them know about the problem, but i also wanted to post it here in case there's a quicker and equally efficient solution rather than having to wait another week without being able to use my computer for the people at Dell to "try" fix it.

Thanks in advance to whoever can help me with this.