Over the years, I’ve had, I’d guess maybe 15 Linksys Routers/Hubs/Switches. IME, the routers seem to fail after a few years. YMMV, but that’s been my problem with them.
If you’ve never worked with a router, before updating the firmware, I’ll go back to what I said before, try changing the wireless channel. It’s the easiest thing you can do and has tends to fix a lot of wireless problems. Especially as more and more people of wireless routers. Virtually nothing can go wrong doing this. Even if it doesn’t help, it won’t hurt anything…promise.
Updating the firmware isn’t that hard, but it can be a bit tricky, making sure you have the correct firmware package, downloading, extracting, updating etc… Again, not that hard, but if you’ve never worked with a router, I’d rather see you change the channel first.
After those, then we can try going from DHCP to static IP. Again, not hard, but it’ll require making changes on all three devices. As well as changing the default settings on any new wireless devices you intend to connect to this router. I much prefer static IP since it tends to be more stable, but it adds another layer of work to setting things up (including anything wired).