Do you Mac products have similar issues of dropping off when they are connected to other Wi-Fi networks? If not, one of the possibilities may be Wi-Fi interference. This is especially common if you live in an area that has a high concentration of Wi-Fis present, like an apartment or condo complex.
You may find something as simple as changing the Wi-Fi channel may resolve the problem.
If Wi-Fi interference is NOT the issue, it may be possible that replacing your 2008 D-Link router would be the next best option. Typically, for consumer networking hardware that is designed to operate 24x7, five years would be the reasonable maximum life expectancy ... even less for harsh environments.