Your Win7 DVD should be bootable. Try using the one-time BIOS BOot Menu key given on the first boot screen, or set DVD drive to boot first: How to Boot your Computer from a Bootable CD or DVD

If it won't boot, then burn a Repair CD: System Repair Disc - Create

Boot the DVD/CD, accept any offered repair. If it won't start, confirm Win7 100mb System Reserved partition (if you have it) is marked Active, then boot back into DVD/CD to run Startup Repair up to 3 separate times with reboots.

If this fails, mark the Win7 partition itself Active to try the three Repairs. Partition - Mark as Active

You can also mark the partitions active using free Partition Wizard bootable CD, then highlight the Win7 HD and from Disk tab run Rebuild MBR, which may preclude the need to run Repairs.

Be aware that GRUB on the same HD can corrupt Win7 beyond Repair. You can copy out your files using DVD/CD this way: Copy & Paste - in Windows Recovery Console