I have an msi wind netbook, and yesterday night it suddenly turned off for no reason, And now it won't turn on.

Can someone please help?

There are plenty of reasons for this. Please be more specific about what you were doing before it turned off. My guess (one of the most common reasons) is overheating can happen when you block or something blocks the exhaust fan of your laptop in this situation you would take out your battery and wait for sometime (4 hours-20hrs).

I was installing windows 7, and it was installing fine then suddenly it turned off, then it wouldnt turn back on.

Is it that it wont boot (like gets stuck in a certain stage in the boot process) or is it that the power button seems to be not working whatsoever?

(Ive got a feeling its pretty much dead anyways)

The power adapter has a LED (small green light) on it? is it on when you plug the power cord?
It might be the power adapter...

Yeh it is on, It just wont boot up at all.

The power button lights up and the fan wizzes then nothing.

Sometimes this happens to my laptop, and I just take the battery out and reinsert it. Then I hit Power, and it's good.

Try that.

I have tried that many times... and it doesnt seem to work, i have also tried 3 different hard drives in it and it just wont boot them up at all.

Send it to a professional repair person. The chances of someone here being able to fix the problem for you is almost zero.