WMP cannot access file error

Help I used to be able to play all my songs and videos but all of a sudden they all stopped working. Every time i open a song or video it says Windows Media Player Cannot Access File. It has a web help button but the info on there doesnt help. It says its cause of proxy or using the file somewhere else but its not. I really need help. Thanks.

I just realized theres a topic with the exact same problem i have