So a while back my main HD crashed and I had to do a reinstall from backups onto a new HD. I have a Brother DCP-L2540DW, and for the life of me I couldn't find the original installation disk, so that might be part of my problem (not sure). I was able to find an installer from the Brother website for my model of printer, and initially everything worked just fine. But the next time I had to use it, my computer was treating it like it was offline. I looked up the issue and found a solution on Google, and it went back to working just fine. But I had to use it again today, and my computer again treats the printer as being offline. The fix from before is still in place, so I've got nothing. :/ I have a laptop, and the printer still works just fine with it, so it has to be a problem with my main rig.
Double check whether the IP address of the printer is changing (it could be power cycles, or it could just be getting assigned a new IP address by your router). I've had similar issues with a wireless Brother printer before. On newer PCs it isn't an issue, but on Macs and older PCs any time the IP address changes it leads to problems (or so I've experienced). It's really frustrating.
By any chance are you running Windows 10? It seems the latest updates have borked a number of things. My suggestion would be to uninstall all the drivers and software associated with your printer and then reinstall it to see if that fixes it. If it doesn't, then I don't know.
Not 100% sure if this will be the same in Windows 7, but go to your Control Panel>Devices and Printers, and then find the printer. Right click>Properties>Web Services. The IP Address should be listed somewhere on there, write it down. Next, go into the network settings on your printer. Again, not 100% if this will be the same, depends on what version of Brother printer, but on mine I go to Settings>Network>WLAN (or LAN)>TCP/IP and it should list the assigned IP address. If this IP address is different than what your computer lists as the printer's IP address, then you've found your problem. The only workaround I know of is to keep manually updating the IP address whenever there is a power cycle or an IP address reassignment. I'm sure there is a better workaround but I've been to lazy to find it (and it only affects my better half's Mac once or twice a year, so it's rarely an issue) You could probably also login to your router to see what IP address is assigned to the printer, and if this differs from either of the above.
Looks like it was slightly different (by only one digit on the end). I changed it on the printer and now it works fine, so I'm guessing it must be set to go through a series for each reboot or something like that.
The router which connects your local area network (LAN) whether it's wired or wifi dispenses IP addresses using DHCP to each device that is connected to it unless the device is given a "fixed" IP address. Alternatively the router should have a reservation table that can be used to dispense the same IP address every time the same device calls for one. Both the router and printer have web based admin pages that can be accessed via a web browser from a computer on the same LAN that allow setting fixed IPs (in the case of the printer) and reserving addresses. Consult the manufacturer's instructions for more details (probably online at their website for support). Printers should be given fixed IPs to avoid losing connectivity with it from all other devices that need to print. The other devices tend to "remember" the last IP address and if it changes, which it will from time to time depending on power cycles and which devices come online first, lose connection with the printer. You'll need to check the router admin to see what range of dynamic addresses it can dispense, and give the printer an arbitrary fixed address just above or below this range. You'll need to update the printer properties on each device that connects to it to have the correct new fixed IP. Or, you can set the router to dispense the same address if it has this feature. If you change the printer IP address back to whatever it had before, you risk duplicate IP addresses on your LAN with whatever device the router gave the address to.
I couldn't figure out how to set a fixed IP on my old router (very un-intuitive admin panel), but I recently got a new router and was able to set it very easily. No more IP reassignment issues!
Older routers don't have the reservation table, but yeah, that's easier than setting fixed IPs on printers if the feature is resident on a newer router. The linksys I was on at home from 2004 didn't have the feature. I think they all do now though.
