From bitter experience, in the days when I didn't know better and tried all you have tried and more, you have a dead or dieing DVD writer.
They last about 3 years, sort of, but can go dud in 3 months in the worst case (whoopee, you get a brand new drive for free!)
If cash is a real problem, then just turn off the 'puter, unplug everything at the back and front, remove the screws holding the drive in the tower (usually two each side, but often only one each side if the guy/gal doing the install was in a hurry or just godamn lazy.
Then find a friend. Lay his/her computer on it's side, take of the case cover on that side. Pull the ide or sata and power connectors off his/her drive, and put it on yours (which you balance on the edge of the machine being very careful that it can't drop in side and hit the motherboard or its components (Tip - a newspaper under your drive covering the whole of your friend's board is a fantasticallly good insulato, dry paper does not conduct electricity at all). Now try a burn. Any software like CloneCD or Nero (my two favourites) will do.
Don't worry too much about speed - if the drive is working, it will work. I fit ain't working then it really is a dud. At $25 a pop, writers have become a commodity. So just go by a new one.
The alternative is a search for the solution to the problem that can last a thousand years.And at the end of all that, you still have to buy a new one. I did that 3 times. Then I got wise!. 10 writers later, I never hesitate. I just go buy a new one. If the new one doesn't work then I have a spare (that never happened), just in case the solution was a reinstall of XP or whatever, but, in 100s of cases, that has never been the problem. It has always been a dead writer.
Oh, unless you need it, disable or remove Nero Scout. All it does is scan your hds for burnable .nrgs or isos or whatever image format. Waste of CPU and disc time. There's an option to disable that in the install and in the repair/change. Or you can disable it in options (from memory), but better to kill it dead.
For the best drive to buy now (it changes every few months), go to CD freaks. Just Google, easy to find. Good site. Need to read a lot, but worth it. You can learn that the dvd/cd writer equivalent of a bios keep a list of all known DVD/CDs and knows their limitations. Depending on the brand or the manufacturer (mostly not the same), it will choose the right speed if you ask too much of it.
If cash is really bad, and if you can handle a screwdriver, you can try a last resort which is to take the drive out, open the case (carefully, its easy to break a tiny piece of plastic). Clean the lens with alcohol and a tissue. Clean any plastic parts the look murky the same way. It MIGHT work. But it probably won't. At least you get to look inside. Educational stuff.