Pump issues, need help (very detailed)

So I just purchased a house, it has an inground indoor pool. I need to replace/fix the pump (I believe) due to the fact that I can't maintain prime ( I think) on the pump that's there now.


The pool is this shape here :

http://www.peakpoolsandspas.com/wp-c...freeform10.jpg

I took a rough estimate on size with a measuring tape and eyeballing it.

It's max is 30 feet by 25 feet and depth is 9 ft on the deep 4 on the shallow.

Providing I'm doing this sheet http://www.poolsuppliescanada.ca/how-to-guides.html properly that makes my gallons roughly 25600 Gallons.

So if I wanted a turnover rate of 10 hours, I'd need the unit to be pushing 3700GPH or 60GPM, I know the pipe to and from the pump is 1.5" PVC so your max flow would be 63GPM @ 10ft/sec.

Currently I have this pump (image :http://i60.tinypic.com/2uq2gs3.jpg)

I personally can't find anything on this, however it's a 4HP pump.

My question is what would you recommend ? is there something I can try/test/check first before I go spending all this money on replacing a pump? I had it running for about 12 hours straight when I first moved in and now I can't get it to keep prime, I can force it to push water to the sandbag and down the washback if I put my hose and a 1 1/2 pvc on the skimmer (removing the mesh) but I can't get it to push water itself...

This is a PAINT photo (best I could do) of my setup, and would be more than willing to answer other questions.

http://i60.tinypic.com/5bw8zc.png

Any tips/advice would be appreciated.