3D printer test troubles (M999 error, motors do not move)
Two immediate issues I can think of are:


Do the floppy drive and DVD drive stepper motors have sufficient torque to turn whatever you have connected them to? You don't say what sort of printer you have built, but a holding toque of 44 N·cm (62oz·in, 4.5kg·cm) or more, is desirable. Maybe you should consider upgrading your floppy ad DVD drive motors to Nema 17 motors... See RepRapWiki - Nema 17 for more details.
Do you have the correct thermistor selected in the firmware? Check your firmware configuration file.


To further check the thermistor, disconnect it from the RAMPS board, and using a multimeter, check its resistance at room temperature. Then compare it with the temperature characteristic graph of your thermistor type. A general 10K thermistor has the following response curve (source):



Does the reading that your multimeter gives, seem reasonable?

Also check the RAMPS thermistor input, by shorting the thermistor pins on the RAMPS board (using a jumper). What is the temperature reading now? It should be whatever MAX_TEMP is defined as, typically around 400°C. Again, check your firmware configuration file.



In addition, M999 is not an error, but a command used to reset the firmware/printer, after an error has occurred.