I cannot print from my computer via network. (For Macintosh)

I'm using my Brother machine in a Windows XP/ Windows Vista networked TCP/IP environment. I was able to print, but suddenly I cannot print. Why?

I'm using the Simple Network Configuration capabilities of Apple® Mac OS X. The printer appears in the "Print Center", "Printer Setup Utility", "Print & Fax", "Print & Scan" or "Printers & Scanners", but I cannot print.

I'm using Windows Vista or Windows 7 and trying to use a Brother machine connected to the network, but the machine stays offline and I cannot print.

I'm using the Simple Network Configuration capabilities of Apple Mac OS X. I can print from a Macintosh, but not from a Windows PC.