http://support.apple.com/kb/HT1434To find out the OS, click on the Apple icon in the menubar>About this Mac.
Sorry, I must be a bit brain dead today. Of course, you can't do that, since the computer won't boot. If you call Apple with the serial number of the Mac, they can tell you what OS it came with and for a relatively inexpensive charge send you a replacement install DVD.
But, unless you have AppleCare, which is the extended warranty coverage, since it's a 2009 you won't be able to get any tech support from Apple, at least not without paying a fee for additional support. What you might do is bring the computer in to one of the Apple Stores (they will at least look at it without a charge) if there's one close enough to you, or to an Apple Authorized Repair.