Q: my friend sold me a macbook pro and now it it seams he h

What happens if you press and hold "Command+R" when you start up? Can you get into Recovery Mode? If so, open Disk Utility and repair disk and  if it still does not boot then use the Reinstall OS X option.

Because t he OS was associated with his own Apple ID. You will need to obtain your own OS copy and install it. Depending on what model it is will be different .

This forum is not devoted to notebook users but to tower (65lbs) "Mac Pro"

Actually, if they deleted the OS, you will need to boot to internet recovery. Command Option R after turning on the computer, it will take a few minutes and require internet connection. Then select reinstall OS X. That will install the OS.

We would first need to know what model MacBook Pro you have. Go to this site and enter the last three letters or numbers of the serial number. It will be on the Mac somewhere. Usually the bottom for a laptop. Please post a link to the resulting page.

That Mac came with Snow Leopard, 10.6.3. You can't do a Recovery, or Internet Recovery install because it would require knowing the App Store ID and password of the account Mountain Lion was purchased through before ML would install. Though actually, you wouldn't be able to do an Internet Recovery at all since that has to be part of the Mac's firmware, and your Mac won't have that ability.

You'll have to go back to your friend and get the original gray disks the Mac came with so you can boot to the DVD and reinstall the original OS, then update it to 10.6.8. From there, you could then create your own App Store account and purchase Mountain Lion for $20, or skip to Mavericks, which would be free.

It's not a sure thing a 10.6.3 retail disk would work with that Mac as the retail disk might not have the hardware drivers on it for that Mac. If your friend no longer has the original gray disks, you'll have to call Apple and order a replacement set. They'll ask for the serial number to make sure you get the correct disks. I think a set is somewhere in the $20 - $30 range.

Mid 2010 computer, the original install may have been the Snow leopard. You may need to get the snow leopard disc, erase the computer again, boot to the disc, reinstall the OS, and then upgrade to mountain lion

I do apologize but there is no mountain lion disc. Apple stopped the discs after Snow leopard. If Snow leopard was originally installed then it will boot to that disc

my wife just found the gray disk of my 24in desktop and the mountain lion disk

The gray disks for a different Mac will not work. It will not have the drivers on it for your MBP and will refuse to boot to it.

If Snow leopard was originally installed then it will boot to that disc

Maybe. Doesn't hurt to try, but if it comes up with a "No" symbol, you'll have to get a set of the gray disks for that Mac from Apple.

Try to put the disc in the computer, shut down, then power on holding the "C" key. that should boot to the disc. Then start the reinstall process.

If you can not boot to the snow leopard disc follow this link: http://store.apple.com/us/product/MC573Z/A/mac-os-x-106-snow-leopard

that will get you to the point where you can get a new copy.