I recently bought and a friend installed a modchip (Duo 2 GT). The installation was perfect to the instructions posed by the site. When the PS2 was put together however, when i switch it on, the LED's on the front and the disk drive work, but the fan doesn't and no image appears on the screen (the blue swirly clouds).

I had it checked by 2 other people and they say that it may have something to do with the power pack, such as a fuse blowing.

Any ideas?

check ur bios instalation... maybe u got a short there...

clean it... if its not working then remove chip clean again... and test ps2 again
if u got same problem then check ur ps2 SMD fuses on board

they got boxy shape and a number on them usually 50 63 and 30