Printing Firmware Problem

Hi there, Ill get straight to the point,
yesterday I installed marlin into my printer, with the right configuration file right here: [reprap.pt] (Exact download link)
(Not to mention I have Prusa I3 Mendel)
The problem is when I installed it onto my printer safeguard turned on and an irritating noise filled the air. With quick reactions I turned on pronterface and tried connecting the printer, The problem M999 occurred and I have looked everywhere to solve it but I cant. Pronterface mentioned that it could no recognise the printer due to the baud rate. In the configuration.h file of Marlin, I updated it to 250000 baud and reupdated the printer. As that failed the printer continued to make its noise. Again I went onto pronterface and connected, the problem was this time that the extruder and bed had reached their maximum heat and where turned off. I configured the file again and made the max temperatures 220 (extruder) and 8-0 (heat Bed). The problem stilled occurred and pronterface continued to give the message that my heat limit exceeded. I tuned the temperatures right down to almost 50 degrees each. But the message still occurred. The M999 problem is still there and I'm not sure how to fix it.

I have learnt the basics of 3D printing so I apologise if I do not understand any complex information.
and I was wondering if sprinter was a good firmware to use?

Did you purchased the printer from someone or did you put it together? did you check that your printer thermistors are correctly installed?

Sounds to me that either you have the wrong type of thermistor set in Marlin or they are not connected properly to the board.

Note: some versions of Marlin had bugs related to temperature readings, be sure yours is a proven stable version.

I am setting the printer up for a friend, I believe he bought it from somebody, the thermistor cables are in correctly, the printing problem only occurred once I installed marlin onto it