|So, you have not recently added or removed any hardware or software other than the Seagate drive? Is the Seagate a USB connection, or something else?|
Are both your optical drives properly identified by the BIOS when you first start up your computer? How about in Device Manager?
What drivers did you attempt to install?
Searching for both of those drives yields lots of hits with folks having problems with them.
Have both of these drives been working OK in the past?
Have you switched to a new spindle of disks?
If both of these drives are connected to the same cable then if one develops a problem it can affect the other one. You could try isolating the problem by disconnecting one at a time. The jumper on the remaining drive may need adjustment if the drive doesn't show after that.
Review all the above possibilities first and then check below.
It is possible an update from Microsoft may have caused the problem. To check what updates have been installed recently go to Control Panel> add/remove programs. Be sure the box to show updates is checked.
You can review the updates by the date they were installed. You can also Google each of the KB numbers to find out what the purpose of the update was.