Iphone 4 not connecting to wifi?

I have an iphone 4. I bought it off ebay, refurbished, two years ago. I know it's old and at the end of it's lifespan. I'm purchasing a new device in a couple days but, in the mean time, I need my iphone to work in order to do my job. I've had issues with crashing aps, but up until yesterday, the wifi on my phone worked fine. Yesterday, it suddenly started one-barring, and randomly disconnecting from my network. I checked with my ISP, and there are no service issues in our area. All of my other devices connect to our home network just fine, with no weird issues. I looked up possible solutions, and tried them all. I restarted the router, restarted my phone, and I even tried the 'forget this network' trick. Now, my phone sees my wifi, shows full strength, but won't connect. Even though I am typing in the correct password, it says 'unable to connect'. Is there anything I can do to make my phone work for the next few days?