My Maxtor OneTouch 4 simply

Question

My Maxtor OneTouch 4 simply does not backup anything! I have it turned on & attached to my PC. It worked before no problem. I also used it to back up from my Mac - no problem except it does not back up sound on short films made with my digital camera. The bulk of my photos & files are on my PC which is not even showing the Maxtor icon in 'My Computer'. The only recognition is when you want to remove it and you click on 'Safely Remove Hardware'. This is very annoying as I have managed to use it in the past. I purchased the machine on the 30Jan08.