Please Help with this issue

A couple of weeks ago I upgraded my OS (Vista Home Premium) to Windows 7 Professional on my Dell Inspiron 1545 Laptop. The system no longer detects the DVDR/CDRW drive. There is no drive letter for it and it is just as though the drive is not even there. The drive is DVD Writer TS-L633 (Model L633B/DEFH). I know that logically there must be a way to fix this problem. After all Windows 7 installed from the very drive it will no longer detect. I have tried updating drivers, firmware updates, BIOS flash, etc. I also pulled the drive and reseated it. Still the drive is not detected as being connected to the system. I am having to use an external USB DVDR/CDRW drive. Please help if you can.

Bill