Insert format disk (What the f@#k!!)

I have just installed a programmed modchip into my ###ne, it is correctly installed i know that much, but when i switch it on it says please insert format disk - why?, what is a format disk??
Please help

[spooky]

Does it say "insert playstation format disk", if so then you have infact installed the chip with the wrong diag or have the wrong code for the diag you are using.