You say that 'nothing else has changed' but you might now being getting interference on your router's signal that wasn't there before. For example, your neighbour could have installed a new router using the same channel as yours. So you might need to go into your router's settings to change the channel it's using. (If you need instructions, we'll need to know the make & model of your router).
However let's start with the simple stuff first. Resetting the TCP/IP stack is really easy and often fixes wifi connection problems:
Click the Start button. Type cmd into the search box. Look above there to see 'cmd' shown as a result. Right-click on that result and select 'Run as Administrator'. When a box appears, type the following line. (Just type from where the cursor is. You don't need to start a new line):
netsh int ip reset resettcpip.txt
Hit 'Enter'.
You'll see a message telling you that you need to restart your computer. Do so.