Where did you get Windows 7? Did you burn the DVD yourself?
Enter your BIOS setup at boot to reset it to defaults. Then check the SATA controller to set to AHCI mode.
Under Boot Order set DVD drive to boot first, then HD. Save changes and exit.
Try booting DVD. Are you prompted to "Press any key to boot disk?" If not reboot and tap the one-time BIOS Boot Menu key given on first screen which is often F2 on Sony. What happens when you choose DVD?
Next try writing the Windows 7 installer ISO to flash stick using Universal USB Installer
with Windows 7 in dropdown menu. Boot under USB, Removable or HD's on one-time Boot Menu with HD set to boot first in BIOS setup.
If these all fail to boot the disk, use free Partition Wizard
bootable CD which will autostart on its own, wipe the HD from Disk tab after clicking on DIsk # to highlight it.
THis will force the installer to autostart to reinstall.
If these steps fail you may have hardware problems. Use the hardware tests in these troubleshooting steps