Acer aspire 5750G Booting problem/disc read error

Hi. Hope to get some help.

I was transfering files (movies, not system files or something) from C to D on my computer, because C was almoust full. Then suddenly my pc turned of. When started, the error message "No bootable device - insert boot disk and press any key " showed up. (Plus some text before that, which I dosen't remember.) Pushing any key or restarting my computer didn't help.

I tried finding a solution online and someone said I should take out and put in again the hard drive. I did this, which resulted in the computer recognising the hard drive. (I am pretty sure it used to say that it didn't recognise it/none, when I pushed F2 when starting the machine, but now it does recognise it.)

Quite soon after this (I might have looked at F2 once or twice more, without doing anyting in there) the error message changed to "A disk error occured. Press Ctrl+Alt+Delete to restart." This obviously doesn't help; the message just pops up after the restart.

So please help :) The computer is not very good, so I don't want to send it to repair just to pay a lot of money. The repair probably will just erase all my pictures and videos as well, so I don't like the idea of that.

Thanks for the help you can give me :)