I have an OS license but no disk, what can I do?

contact ms or apple (whatever OS mfc it is) and show them the proof of purchase...if its legit, they will send u the cd....otherwise, you will need to buy a new OS.

Unfortunately, you probably got duped - the previous owner may have told you the license to the os was yours -b ut if that were true, they would have included the CD - instead, they probably kept it and installed that on their new pc (or kept it just in case they needed it), so because of THAT alone, it is possibly that you really do not have a license to use or install that OS and may need to buy one anyways.

The OS should be on another partition of the hard drive. Go into Explorer and you should find two partitions, one called C: and another one called D:

You can also obtain os install cdrom disc(maybe dvdrom disc) from your friend. Or Where you bought pc.

it depends on what the os is. ms has stopped providing replacment disc for xp they're only doing replacement for vista now.