Poor wifi connection - PC: 5 bars, Router: 1 bar

I would guess that you have turned up the transmit power on the router too high. While this increases the range that the station can see the router, it doesn't make it any more visible to the router.

This is a mistake often made by users with wireless when they are trying to increase coverage/range. Since most consumer wireless use is heavily weighted to download, a certain amount of transmit power increase will often help.

However when you wind up in a situation when the station can easily see the access point but the access point cannot see the station, you run into a situation where the ACKs are not getting back to the AP and frames start getting re-transmitted. This can seriously impact performance.

The other option is that the transmitter on your station's wireless radio has started to have issues. While it can hear your AP just fine, it isn't transmitted well anymore. I would lean towards the first solution as being more common though.