Q: my macbook pro wont boot for no reasson at all

no problem...let me try to help you...don't worry, I'm licenced to handle crazy....you could start out by rebooting and pressing command+ R (that's the cloverleaf key and R) to start up from the recovery partition. From there, go to the centre of your screen, and then go to OS X tools, then run Disk Utility and repair hard drive, then set your original hard drive as the startup disk, then reboot. Hopefully that helps somewhat. Failing that, try zapping the pram or resetting the SMC/PMU, instructions on how to do that can be found on Apple's support webpage, or if you can't wait, like me, yahoo or google works okay.  Target disk mode works if you have another mac to connect to....on its own it doesn't do much of anything. You could also try starting up in single user (safe) mode by holding down the Shift key on startup....

also, holding down the option key will show you all potentially bootable hard drives. Usually to start up from a snow leopard disk, you'd put the dvd into the drive, then then reboot and hold down the C key. It may take a while, but keep holding it down until it shows the snow leopard startup thing. If you suspect that the dvd drive may be giving you trouble, using a dvd cleaning disk with the brushes built into it, or a shot of compressed air may be helpful as well

good luck

JB

... im truing to upgrade to snowleopard with a disk

What disk?

Describe it, or take a picture of it and post it in a reply.

To boot from the optical drive press and hold the c key while you start the Mac. You should hear it make some noise.

What exactly happens when you try to boot up?

Does power light come on steady?

Do you hear the startup chime?

Anything show on screen?