My Sony DVD writer reads CD and DVDs but...

Could be a faulty burner.
Could be software.

Possible solutions
1. If your not using Nero to burn, install that and try.
(Im sure you can download a demo to test it)

2. I'd also uninstall any dvd ripping software...eg DVD43, etc as I have seen problems where that software has stuffed up filters, meaning the burns always fail immediately. Other times it has caused the burner to no show up in a burning program.

3. Id also click start, run and type MSCONFIG and press enter, then disable any items in the startup panel that are not related to your burning program. also do this for the services tag. (Click hide Microsoft services first)then reboot and retest. If the burner now works then some software is definately causing the problem

To restore normal boot, run msconfig again and choose normal startup.

4. You could also try booting from a dos boot disk and try burning something with that... eg use a ghost boot disk to make a system image. if that works then its definately software.
If that doesnt work then I'd say your up for a new burner.

5. If you have a test burner, try it with that, you may need to do one reboot after first install. It wont need any software, as support for cd/dvds is built into windows. If the test burner works your old burner is faulty.

If that doesnt, You have a software problem.

Before replacing it I'd clean the lens...but its not likely to fix anything if it still reads ok, but has been known to help.
You could also try flashing the burners firmware...not for the fainthearted but what have you got to lose.

IF IT IS SOFTWARE
Then isolating it can be hard.
1. use nero.
2. try checking your filters....http://www.kalytta.com/tools.php has a freeware tool on that page that claims "This tool is able to detect and deactivate or remove broken (unloaded) Filter Drivers.". I havent tried it though
3. last option - run a repair install over windows... this will keep all your programs and files intact but replace all system files and redetect hardware. Google windows repair installation for more info.

Sorry I cant be more specific..but there are sooo many causes of software corruption

HT JoshAU