I have a Dell computer desk top. It is probably about 6 yrs old. A couple of years ago I got an apple computer and disconnected the Dell, disconnected the monitor, printer, speakers, etc and stored it in a closet. Soon after I spent about 2 years in and out of the hospital. Now because of important files I have in the Dell, connected it, and trie to start it but nothing will come on except the green light that indicates the power is on. Nothing else comes on. The screen is blacken, no fan, nothing else. What can I do to get it to boot up ???