Urgent help pls. dvd play/burn probs

Hi all, am new here My problem begins as so… i have been burning cds and dvds as well as watching them on my puter for bout 5 months. The other day, after burning a dvd the night before, i went to watch dvd in wmp 10, and got error message to change my display settings, which i did but it made no difference. Then i went 2 check graphics driver n its now up to date, still no difference. Im sure i have decoders/codecs present (unless they’ve somehow been damaged) as i have watched & burnt dvds for months. I’ve tried my wmp10 settings, no change. Whilst this has been happening ive still been able to burn and rip dvds no problems.
NOW- i attempted to update nero from a cd which prompted me to uninstall then re-install new version, which i did, but before it could finish installation it failed (due to out of date serial number) and left me without nero at all. I did a system restore to just before this happened, and it bought nero back but now it doesn’t work. It won’t burn anything, my drive speeds are much slower, show time wont work, nothing. It goes to burn, seems to get through encoding, but takes much longer, then gets to burning and always fails. I have reports if anyone can help!!! Please! I’m lost without my dvd player/burner.