Some manufacturers doesn't deliver the OS, or a system recovery on CD/DVD, but instead have it on it's own partition on the harddrive. Usually with a program in Windows to make the disks yourself (which you should do in case of a total failure). So deleting that partition isn't a good idea unless you have backups. To invoke the system recovery, you usually do that either from a program in Windows, or by pressing a hot-key before boot. F11 or F12 for example, or from a menu inside the bios. If the recovery partition is still there, but you can't access it from Windows, or by the afore-mentioned methods, you can use a partition manipulating program and set it active, and then try to boot.