Firstly, please ensure there are no bright sources of light shining onto the ActivBoard. Direct sources of light hitting the ActivBoard can have a significant effect on the readability of the projected image. If your ActivBoard is located near to a window, it may be ideal to close the blinds. Some users even go as far as to install blackout screens if the direct light is too strong.
If the image is still dim, check your projector settings and ensure that the lamp has not been set to Economy Mode. Please refer to your projector manual for further details.
Projector lamps do degrade over time, and as time passes they may gradually dim. If this is the case, it may well be time to replace your lamp. Trying another lamp from a known working projector will help to diagnose if this is the case. Either the lamp could be coming to the end of its life, or your projector could be in need of an optical clean.