Why does my Acer laptop keep shutting down on its own?

I have an Acer Aspire 5755g that will sit and run fine on my desk but whenever I try to lift my laptop to another location it will randomly shut down. It is not overheating because I can turn it back on straight away and it will sometimes happen if it is the first time I have turned it on for the day. The only thing that causes the problem is when I lift and move the laptop. It can sit at a desk fine or I can even bump/tap the laptop case on purpose and it will still run until I lift/move it to another location.

Windows 7 64Bit ultimate. Fully charged battery.