Machine was shut down and power off for 4 weeks while away.  Tried to start, but  get  no image on monitor after pushing start button . disconnected monitor and get test pattern ok.  On startup, I get blinking green light next to start button. On the 1234 light pattern on rear panel, I get AGAG and then GGGG.  There are also 3 beeps followed by 2 beeps about 3 seconds later, while trying to start.

I'm a real non techie who would appreciate any help.

Ed