You'll either have to use the windows installatio CD that came with you PC to re-install windows (If you dont have one it might be that the manufacturer place a recovery partition on the HDD to store the re install files, try hitting F11 repeatedly during boot to boot into it). If you lost the disk or deleted the partition, then it may be possible to purchase a recovery disk from the manufacturer, try contacting their custome services.
If neither of these are possible, then you'll have to find a linux distro that you can burn to disk and use.