Divice manager only looks at the function of the drive ... not the health
two easy things come to mind
1 .... you've somehow chanded the settings in the prog you use (nero????)
2 .... the discs are 2x burners (look on the side of the box
3 (?) the discs are (to be polite!) economy ones ... which whatever they say on the box will only burn at 2x
In the past I've bought a box of cheap opticals ... which wouldn't work with my burner at all ...
donated to a friend ... they worked fine
the last option is that the burner is on it's way out ....