Below are a few things you may want to check.
1. Make sure your DVD-rom is still detected by the bios under 'advanced'/SATA Configuration.
2. If you can still boot to your hard drive, make sure you can still read DVDs inside Windows if you haven't tried this in a while.
3. Try tapping the 'ESC' when the ASUS logo appears to get the boot menu, or make sure your boot option priorities are set correctly.
4. It shouldn't be too important, but if you don't want to see the PXE message, disable the PXE ROM boot to LAN function under the 'boot' menu of the bios. If there aren't any bios settings you are worried about keeping, consider loading the bios defaults and changing your settings from those.
Hope this helps.