MacBook Pro randomly shut downs.

I have a MacBook Pro (17-inch, Mid 2010) that I am having some problems with, it shuts down randomly. I don't know what it could be, there doesn't seem to be any rhyme or reason to it.

The computer shuts down immidiately if I try to run a program. otherwise it may shut down at any time. It can run a long time if it's not beeing used / operated

I've tried:

- Removed the fans and cleaned them.

- Disk Utility, repear.

- Safe Boot:

- Single User Mode, fsck -fy and got "Appears to be OK"

- Deleted and reinstallation Mavericks.

- Reset the NVRAM

- Run Ccleaner

- Resetting the System Management Controller (SMC).

- Download temp & fan monitoring app (Temperature Gauge Pro)

and got:

Fans run at 1999 RPM.

all tempratuerer is between 32 C to 60 C, except GPU Diode (Analgo) who have 127 C..

Anyone who knows what the problem might be?