Possibilities for a broken laptop

So basically I have inherited my brother's 2-year old HP Pavilion M6 laptop that does not work. It apparently has a broken motherboard (it has already been replaced once and then broke again). I took the liberty of dismantling the laptop and I have reached the point where I'm not sure what I should do moving forward. I need to have a laptop for college next year so I'm trying to see if this laptop can help me out.

The way I see it, I have three options now: I can sell the laptop parts that I have removed (4GB DDR3 RAM x2, 750 GB Hard Drive, Intel i5 3210M processor...), try to buy a new motherboard and rebuild this laptop, or use these parts in a completely new laptop build. I have some knowledge of computers but minimal hands-on experience, so my confidence level with building a laptop is like 70%. I also have $700 to put into a laptop, in case that is important.

I'm also wondering if it's possible to change the motherboard out for another one that would allow me to use a 4th gen i5 or i7 in this laptop case since I would like to upgrade the processor if possible.

Long story short, I guess I want to know how much money I could potentially get for the parts and how feasible it is to build a laptop using these parts. Any advice would be greatly appreciated!