IS the CDR readable in other drives? the first thing to check is that the burned disk itself is not corrupt. you can also check this with a freeware program called CDCheck. although if your burner wont recgonze the disk you will have to use another system to run the program and check the disk. if the burner recognizes non burned CD's then it is probably the disk itself that is the problem.
if the disk is not corrupt, then it is either a windows file system problem or a hardware problem. ( the drive itself.) if it is a windows file problem uninstall the IDE channel the drive is on and reboot, when windows restarts it will automatically reinstall the IDE channel and the drive.
Also make sure that the disk in question was not burned as a multi session disk and has not been finalized.