From my research on this printer (reviews are awful) it should be noted that by itself it is NOT wireless capable.
"The 926 printer by itself, does NOT have wireless. You can attach it to a Dell Wireless Printer Adapter 3300. The 3300 uses your wireless router to transmit everything from each computer to the printer. No need to have a host computer turned on to print. If you have a desktop, on your network, you can install the drivers, choose network and then tell it the printer is connected to a wireless print server and you'll be able to print from the desktop, even though it's wired. I have the 3300 attached to my Dell 964 Printer and it works great. If you decide to purchase the 3300, when you get it, please post back, or even use this thread, and I'll be more than happy to help you set it up with instructions." This is from the dell site.
To the O/P if you have the users manual (given that it has worked properly in the past) my suggestion would be to disconnect the printer from the computer/uninstall the current software/then with your manual in hand follow the guidance PRECISELY to reinstall the printer. If you do not have the manual it can be obtained (free) from the Dell site. Just before doing the uninstall/reinstall if you haven't already done so you might go to the Dell download site and install the latest drivers for the printer from there. Do the other functions of the "all-in-one work properly? truenorth