Why is my Samsung Q35 Laptop power off while working

1. Whenever I am using my laptop made by Samsung, Model is Q35, the computer will just power off, and if I try to switch it on at that moment, it will not working.

2. Sometimes, if I have used the computer for so long like 2hours it will become very hot at the bottom and will just power off. If I try to switch it on, it will not work.

3. If I am switching the laptop on, the screen will go dark, I will have to do open and close for about 3 to 4 times before the screen light up.

I bought the laptop in 2007, and about 6 months after it fell from reading table and the hard disk crash, and it has to be replaced by Samsung, since then, I have been experiencing the above problem in 1 and 2 above.

The 3rd problem started last year June 2009.

Please any help as the laptop is now out of warranty since 2008 and I cannot afford to buy another one now as I am still in the University.

Thank you for your advice in advance.