Since you can open some DVDs and not others, there could be a fault in the DVD Read/write program that you are using. Try three things - (1).Uninstall the existing DVD Read/write program eg. Power DVD or Nero Suite or whatever, and then reinstall them and then see if you can play/open the Feb. Digit DVD or not. If not then try to remove the ancillaries to the main DVD Read/write programs one at a time and test the said Digit DVD s,say you are using Nero Suite and it containsIn Cd+ In Cd Reader +Photo Show + Templates, first try you Digit stuff without In Cd and see if itopens now, if not now try without In Cd Reader also, if not successful, next try without Photo Show also etc.
(2) If the first step does not help, next try opening the DVD with another DVD Read/ Write program that may be on you PS thpughitis not your default one and see if that works- if you do not have any other program you can look for one in Dighit Feb '06 DVD ( it has a couple of these).
(3) If none of the above helps, then try to (a) update the driver/fireware of your DVD Combo device from the manufacturer's site; (b)See that your DVD Drive has DMA support enabled; (c) See if your Combo's manufactureer has on offer any patch from their site andif so download and install it and at every step check the stubborn Digit DVD- 99 out of hundred it seems you are facing a software glitch and it is not a harware problem- I don't think your DVD decoder requires any updating.
Finally if you are successful in opening that Digit DVD please inform others on the forum. Trying the sid Digit stuff on someone else's PC will eliminate the doubt of a defective DVD disc.
PS. Someone has suggested cleanig your DVD drive- I would love to learn how it is done.