[spooky]

Sounds to me like you may have blown a fuse while installing the mod chip.

All PSX models have a main fuse on the power supply board, this is probably ok but worth checking, the rest of the fuses are located on the PSX motherboard.
There are about half a dozen of them and they dont look like normal fuses at all. What you are looking for are small black cubes that are soldered directly to the board, they are about 3 - 4mm square.

You will need to check these with a multimeter and if they are open circuit then either replace them or solder a thin link wire across both the terminals. I would recommend that you try to replace any blown fuses with one's of the same value as the help to protect different parts of the board, the trouble with using a wire link is that you dont know the current rating of the wire. It wont cause any problems to the normal running of the machine but if things do go wrong then the wire could take longer to blow than a correct rating fuse, and more damage could be caused by this.