I have shared printer attached to my PC that I access from my laptop via a router. I had been able to print fine until a few days ago when the printer is showing as being offline on the laptop. I've checked all the setting to be sure it was set for Sharing, etc.
My PC is a Dell E4500 running Vista. My printer is a Brother MFC 440CN
When you try to print and the printer is not available Windows will automatically mark it as offline. To reset it, right click on your printer icon and then click on the line "Use Printer Offline" to remove the check mark.