Does not charge

Yesterday, I was charging my Sony Xperia T for the night and the next morning I noticed the battery wasn't charged at all. The red light was still on though, but every time I started the phone it would show an empty battery. At first, I thought there I didn't plug in the cable correctly...

Dear Community, I have the following PC spec: Intel Core 2 Quad Q6600 2.4 Ghz GIGABYTE P35-DS3L 6 GB RAM NVIDIA GeForce 8800 GT I wanted just to upgrade my video card so something a bit better and wanted to know if it will be ok or due to the aging computer it might be risky? I was thinking...