Combination CD/DVD drives have two separate lasers that work at different wavelengths. These lasers are mass produced and considered disposable hardware. Frequently one laser or the other will fail.
Long and short is that if the drive works partially then the issue is either a dirty lens or a failed/failing laser.
You could try a cleaning disc for DVD players, trying a different make of disc or burning at a lower speed.
You say "it burns discs ok" but that is probably only your software that is indicating that - try the above suggestions.