Entities work in individual projects but not in single project together.

Hello every one

I have created multiple entities, that work individually in individual projects, but when I combine all the entities in to a single project some entities stop functioning. When I compile and run the project with multiple entities on my DE1 cyclone 2 board, entities take chances not working, but sometimes all of them work but when I compile again without changing any thing in particular it doesn't work ect.

More detailed:

I coded in VHDL an audio player, music saved on the SD card, that can be controlled through the RS232 communication board - works perfectly in own project.

I also coded in VHDL a temperature display, that uses the 4 7 segments on the development board, that "looks up" a 8 bit value, that is generated by the switches, and outputs the corresponding values for the 7 segments. This part also works perfectly in its own project. But as soon as I combine these in one project one or the other or sometimes even both stop working.

I only use 10% of the logic elements and 2 % of the ram (when no signal tapping is implemented)

if some one has any idea what the solution to my problem is, please comment.

Arno (student at the University of Pretoria)