34 led: Memory modules are detected, but a memory failure has occurred.  Remove all memory and reinstall only one.  Test each memory individually. for this old model, better replace cmos battery w new cr2032.
Its been raining in my region soo much and my brother is having a issue with is 755 where it just shows amber light for a long time until he presses and holds the power button again and again until the pc shows green light with 34 lights on and then the motherboard starting. Anybody who knows the solution. I have an opti 7090 and its been working like charm and right now he is using it for his college purpose
Dell Optiplex 755 Solid Amber Light