As Akronix has said, you've wiped your Windows installation. If you need to recover personal data files, your only hope at this point is a tool like PhotoRec, which scans a disk for signs of files and extracts them to another disk. If this is your need, stop using the disk immediately!!! Every second you use the computer as it is now, the odds of it overwriting an old file goes up. Boot using an emergency disk (on CD-R or USB flash drive) and do your recovery from there. Note that there are Windows tools that are similar to PhotoRec and that may do a better job than PhotoRec for recovering files from NTFS, but I don't happen to know what they are, so I can't point you to them. Asking on a Windows forum may be helpful. If you have lots of money and your data are particularly valuable, there are professional data-recovery services available. I don't happen to have any specific recommendations, though.
If you don't need to recover personal data files, your best bet is to shrink your Linux partition and re-install Windows. If the computer came with Windows pre-installed, you may need to pay the manufacturer or Microsoft for recovery discs, although this page offers some suggestions about legal downloads of Windows 8, so you could check those options first.
Moving forward, let this be a lesson on the importance of keeping backups.