Wont play commercial dvds

Question

After a full reinstall of winxp home and converting from fat32 to ntfs on the 30g drive, I realised the fat 32 drive would not recognise dvd movie. I reinstalled from the Toshiba oem discs, I did full updates on miscrosoft update on custom setting. Installed codec pack and tried a dvd which wouldn't play in winmedia11. Tried inter-video dvd player but it would not install from oem discs. Then installed avs dvd player. Now plays copied discs but not commercial discs. In media player it shows all of the root menu but you cannot play the files. In avs dvd player the copied disc worked fine but your commercially available disc will not load up. All I hear is the dvd-rom/cdrw seeking. I have searched seemingly everywhere on this problem but have drawn a blank. Can you advise? Laptop otherwise is ok.