mac book pro snow leopard issues trying to reinstall

hello people im new.. new like boxed new to this.
i had a problem with a mac book pro from a friend

it wasnt gettin to the GUI. instead was always on gray screen

after a while scratching my head i installed OS X on a hard drive connected via usb, sucess, then i used migration assistant. to migrate averything from the internal disc.

then i tryed to reinstal on the internal ssd. but i wasnt able, it gave me an error almost at end of the instalation.

i tryed to erase the disc.. but i couldnt i wasnt able to unmount, just to ry i removed the ssd and connected via usb. and VOILA was able to do all.. partition erase, mount unmount bla bla

i erased it then pot it back in, and tryed to reinstall but no luck, this time hanged almost right starting and an error poped up. then i connected the ssd back on usb and proceeded to reinstal. and success.
then i put back in.. but no luck does not boot, it crashes with kernel panic

some ideas please? im starting to become bald... thanks in advance (and by the way sorry for my eng. is not my native)

hi again.. maybe i should upload some poor girls photos to get some answers... but better than that.
a little bit of history:

the mac starte with the problem, trying to open documents.. not doing other things.

I take it you got your MBP used from a friend or is it your friends? If it was new I would say take it to Apple.

You are saying when you take out the Internal SSD and put it into a USB case, the drive works fine but not in the MBP? That sounds like either the Cable to the drive or something with the SATA controller. Both Guess's by the way.

How old or new is this MBP?

is it my friend. isnt new. has around 3 years already. today i tyed to replace the ssd for a hdd i got, installed internal. and i erased any partition so was unpartitioned, i started the installation go to the disk utility and tryed to partition.. and i wasnt able, POSIX error sayd wasnt enough memory to allocate... i got the same error when i took out the ssd out and connected trhu usb, i erased it and put it back in trying to reinstall...so yes there must be some problem on the controller or cable. or something else.. i wonder if a firmware update could fix this. ill try with one of the external instalation i did to update firmware..thanks for the answer i still with my ears and eyes open for sugestions.. THANKS DTRAVIS7

(BTW THE disk i tryed internally was a traditional hdd samsung 320gb)