Assuming this is recent and unprovoked by any physical changes you have made, and the CD drive hasn't died! They do occasionally.
There are two places where you can expect to find the drive acknowledged.
On boot-up press delete several times before Windows starts to load so that you have the BIOS screen and make sure the drive is mentioned there along with your HD. If it doesn't show in the BIOS it has presumably become disconnected inside your box.
When Windows desktop is complete, look in Device Manager > systems > devices and see if the CD drive is listed there. Check (right click) its properties, and no warning yellow triangle.
If all these seem OK and the light comes on (if only briefly) then I suspect the drive has died.
You could still try a cleaning CD but I have never cured one with this.