Boot into BIOS setup to reset to defaults: Clear CMOS - 3 Ways to Clear the CMOS - Reset BIOS.
Then boot the DVD by tapping the Sony f2 one-time BIOS boot menu key. Does it prompt to "Press any key to boot disk?" If not burn another DVD for your licensed version from Step 1/2 of Clean Reinstall - Factory OEM Windows 7
Once you can boot a disk open a Command Line by pressing Shift + F10 at first screen of booted DVD, then Mark Partition Active
the WIn7 partition or it's 100mb System Reserved partition (preferred if you have it). Then run Startup Repair - Run 3 Separate Times
If DVD still refuses to boot (user error is 99% of the cause) go back to Steps 1/2 of Reinstall tutorial to write latest official ISO to flash stick, try booting it under USB, Removable or HD's.