Up until yesterday afternoon, all was working well with my system until quite suddenly my mouse and keyboard both stopped responding. I switched the USB ports they were plugged into and they started working again and I went on my way. A little later I started getting a USB error, Unknown Device. So I unplugged all USB cables except for the mouse and keyboard ( hard to use the system without those guys) and the error went away. I was able to later last night to plug in my digital camera and download the pictures without recieving an error. This morning the system was working just fine but after coming home from runing some erands, the mouse and keyboard wern't responding again. I've tried changing the ports the mouse/keyboard are plugged into without any success. I haven't added any programs or made any changes to the system since my RAM upgrade back in early March.