Bizarre Neo Geo Pocket Color Problem! No Color in my NGPC!

Ive owned this NGPC for years. After a little sort out and tidy up I decided to have a quick go on it, but I didnt get very far...

Its decided its a Black & White unit, but without the power of Black & White unit (or colour for that matter)
It displays most images in either dark grey or complete black, to the point where its unplayable.

Sonic Pocket Adventure just wouldnt boot, I saw some text on the screen whic h was incredibly hard to make out.
Slow shutter speed camera tricks showed that it was moaning the game is for Colour units only...




Next up was Neo Geo Cup 98 Plus, the colour version... Which was even worse!
This one only had black displaying, far from playable, the title screen wasnt even readble and no players would show up in game...



Does anyone have an idea whats up with this unit? Its definately not the games, I tried them in my spare NGPC and they run fine.
Ive also tried new batteries and alsorts, however nothing seems to fix it.

Thanks in advance!

remove all batteries, coin battery included and let the system rest for 5 minutes.

Clean the cart slot?

Thanks guys, Metallizer's fix worked a treat

IIRC from the old SNGP forums, there was some way to glitch the system and put it in that state where it thinks it's a black and white unit, can't remember how it was done though. Never saw what it looked like, thanks for the pics