What that means is your firmware can't find the bootable drive or partition that's set as the startup disk.
It could be it just forgot and you need to remind it, or something seriosuly is wrong either in hardware or software on that drive.
Hopefully it's the easy fix, hold the option key down while booting and select the boot drive, click the arrow, then head to system preferences > startup disk and set it. it should work hopefully.
If not there, it's something more serious and you need to review these links accordingly in sequence given (IE #1-15)
This link here is if the drive works, but can't be booted and you need to recover data off the drive before a complete Erase and Install or taking the machine in for service where the possibily is the drive will be replaced.
If it's a software issue, it might be the drive still works, just OS X isn't bootable anymore. Step #5 should tell you that.
If it's a hardware issue, the drive or a cable, or the Mac might not be working anymore.
If it's a hardware issue that's not your drive (you won't know unless you can pull the drive out and use it with another Mac to test it) if the drive itself is dead then you have lost all your data on that drive, unless your willing to pay thousands of dollars for platter recovery services.
No, the OP is going to have to buy the Snow Leopard disc, I would think. About $50. From Apple, Amazon, Apple Store, etc. I've never heard of the Apple tech's doing a free re-install of the OS if you don't have the original disc(s). Snow Leopard was only one DVD but, depending on what else may have been on the OP's original install disc(s) (iLife, etc.) he/she is just hosed.
Not to rain on anyone's parade...
When holding option down all i see is my mouse on a white screen.
Is it possible to get the OS X DVD online? i seem to have lost mine..
There are two versions of the 10.6 disk, the machine specific ones that came with your Mac (if it came with 10.6) and the $29 10.6.3 retail version. (no iLife)
If your Mac was upgraded to 10.6.3 via the $29 retail disk, then just order another one online at Apple.com, it should come the fastest if available. One can extract iLife from the 10.5 disks using Pacifist from Charlesoft, or buy another iLife from MacAppStore.
The 10.6.x machine specific versions have the free iLife included, came with your 10.6 factory Mac and are preferred to get these over the $29 10.6 retail disks, however if your machine came with 10.6.3 or later from the factory, then you have no choice but to get them as they include hardware drivers not on the $29 10.6.3 retail disks.
If your machine came with 10.4-10.6.2 you can use the 10.6.3 retail disks and get them right away online, no human required.
If your machine came with 10.6.3-10.6.8 then you have to order the machine specific disks.
If your machine came with 10.6-10.6.2 then the choice is optional, either way.