Uploading to Arduino UNO R3

I just tried uploading to my Arduino and its giving me the error "avrdude: ser_open(): can't open device "\.\COM7": The system cannot find the file specified." I used it 5 min before and it worked fine. So to fix it, I tried restarting my computer and re-opening the code and I connect the usb to my computer but it doesn't recognize it at all. I tried connecting it to another computer and nothing happens. So i connect another Arduino and it works fine, my computer recognizes it with out a problem. In my Arduino, the ON LED is on and the L-LED is on but solid. Can someone help me and tell me what may the problem?

Thank you
Saldin

(deleted)

I was working with a motor that required 15 volts... I may have somehow connected it to it... :sweat_smile: