I still think burning DVD at 1x is not posible with this writer unless you tweak the firmware massively....
Probably you burnt DVD-R at 2x and DVD+R at 2.4x - that would be possible.
You burnt a bootable image to the DVDs, right?
So please insert such a DVD, and try booting from it.
Remember to force booting from the ODD according to your BIOS/info.
If that fails, the burner could have a problem, maybe some dirt on the lens(es).