This is problem and a solutions posting.
Dell 530 desktop would not boot up. The screen was black. The unit woud beep four times or is beeping four times. Blue light was solid.
Looked up problem on forum.
Turned unit off. Removed power cord. Removed side cover. Removed graphic card. Removed all memory from slots. Replace all memory. Installed graphics card. Replaced cover. Connect power cord.
Unit started normally.
Hope this posting helps someone else.
You sir, are a hero.
Just had same issue with an Inspiron Athlone thing - took cover off (power lead out first) took memory and graphics cards out, put 'em back in (gently does it), power cable back in - PC now runs fine!!!