Issues testing 3d printer (m999 and more)... need help quickly for school project

Hi! I've been recently building a 3D printer and I'm having issues testing it.
This is my hardware:
Ramps1.4
Arduino mega2560
4x Pololu Motor shields a4988
1x Nema17 extruder
2x floppy stepper motor
1x DVD stepper motor
Generic hotend with 0,4 nozzle
Then I assembled everything and I started testing... I tried ramps test code and it didn't work (motors did not move, but I'm sure they are ok), then I tried using marlin and pronterface; it showed hotend temperature stuck at 150 degrees, but the hotend was not hot. Moreover motors would not move.
I also tried repetier host and it returned me a m999 error without any further explanation.
I had no problem installing firmwares on the arduino and the fan of the hotend is working. I also tried changing baud rate but it seemed not to work.
I need a quick help since this is a school project I need to have a working printer before next week (13 days max). I'm asking for a fast solution to this problem.
Thank you in advance and sorry for my bad English.
I've also attached a photo of the hardware

You should start with the Rampstest program and only the Nema 17 motor.
Did you place all the microstepping jumpers under the driver?
Did you check the Vref of the driver?
Does the motor hum or vibrate?
What's the spec of the powersupply? Is it strong enough to drive the steppers?

What @o_lampe said, plus...

Hot-end temperature is measured by the thermistor... check that that is wired up correctly, and that it is the type of thermistor that Marlin expects.

The firmware will stop the extruder from working if the hot-end temperature reading is below 160? or so degrees.

M999 is not an error code. M999 is a command you can send to reset the firmware after an error. Try looking at the "terminal" window to see the actual messages sent to/from Marlin. Trying to extrude with a low temperature can cause this.

Changing baud rate probably won't make any difference... it's a virtual serial port over a USB connection. If you have communications working between Arduino and your computer, then you shouldn't change the baud rate anyway. Either it will work just fine, or it won't work at all.

Are those little floppy and DVD steppers 12V? Try plugging your extruder motor into the X.Y, or Z connector to see if it will move when an X,Y, or Z movement is commanded. I don't think those little steppers will be powerful enough to be useful anyway.

Quote

Are those little floppy and DVD steppers 12V? Try plugging your extruder motor into the X.Y, or Z connector to see if it will move when an X,Y, or Z movement is commanded. I don't think those little steppers will be powerful enough to be useful anyway.

They only care about the current, not input voltage. I've made a DVD-XY plotter/laser engraver with those DVD steppers and set the current to 100-200mA. The torque comes from the leadscrew/spindle. I even thought to replace the spindle with an M3 lead screw, but never did.