You are limited as to what you can do if they didn't provide you with a Win7 DVD. If so, boot into it, select Repair My Computer on second screen, then click through to Startup Repair and run it up to 3 separate times with reboot to get Win7 started.
If this fails you may need to do a clean install with DVD, which will be a better installation anyway than the factory install. Clean Install Windows 7
If you weren't provided with a Win7 DVD, then you'll need to call the manufacturer's tech support which is always included for the first year. They will likely walk you through recovery to factory condition. Ask them to provide you with the disks. If you can get a Win7 DVD, you'll be ahead. If not, see if you can locate one to do a superior clean install.