Depending on what type of file it is (avi, divx,xvid,mpeg) you can get other players that will play your files. if you can get the codec that can go with WMP then you will be able to advance in the clip..
Here are some Programs that you can use to get the codec that you need Divx Player, Vidomi these are the two that i use
Have fun and i hope this is useful
Motherboard:Gigabyte GA-8KNXP SATA 8X/4X AGP PRO
Processor:Pentium 4 3.4
Video: NVidia TNT2 RIVA, Sound Blaster Live
Ram: 4 gig of Kingston DDR Ram (3200)
Hard Drive:maxtor x2 120 gig ATA133 w/ 8meg buffer