You can open the case to check the ribbon cable and power cord are properly connected.
You can check in Bios to see if it is recognized.
You can check in Device Manager to see if it is listed there and if it is reported as working properly, or other wise.
Since you didn't give any info about your computer, operating system, etc. that's about all I can offer.
Best of Luck
I have a Emachine computer and for some unknown reason my a: drive has stopped working. When i try to save something using the A: drive, it says that i don't have access to it! It is driving me crazy and i have just typed a 3 page paper and i can't save it on my disk! Please someone help me!!!