Trying to fix a xbox but got no luck.

Someone brought me his xbox for me to repair but I can't find what to do.

I modded the xbox 1 year ago, it was working fine from there but now there's two problems (maybe they are linked, I dunno).

First thing :

When I plug my High Definition adapter everything turns to black and white.

Second thing :

the xbox won't run backups anymore and even worst, it won't load evox most of the time, in fact, without a boot disc the xbox only reboots and reboots again.

I tried reflashing the bios, it worked (I mean the flashing), but all the problems are still there.

I really need help on this one. Thanks