Dell Laptop Hard drive not detected

Hi,

I have Dell Inspiron N51100 which given error stating 'Hard Drive not found' some times. This error does not occur every time i boot my laptop. Some times after getting the error if i shake it a bit and start it works fine. I understand removing and placing of hard drive may resolve this problem, but i want to know about below details:

• Even though my laptop was never dropped what could be the cause of this issue?
• Do we have any option to verify re-planing hard drive will work fine and there is no need to replace the hard drive with a new one?
• I do not have any experience of working with laptop hardware but did work a lot with the hardware of desktop (Even replacements/repair of some parts which does not function properly) I want to troubleshoot this problem myself. But it is a very complicated task and I need an expert to get this resolved?

Thanks,

Shailesh