How can computer hardware be damaged?

I have a HP Pavilion Laptop. We took it to a repair man and when he returned it, the computer turned on for a few sessions but now doesn't turn on. It makes the video error BIOS – one long beep and two short beeps. Sometimes it turns on and sometimes it doesn't.
I was wondering if it's a problem with the hardware or not? And if it is, could the hardware be damaged by the repair man playing with the software of the computer or the actual physical pieces (he also removed and re-attached the keyboard).
