Windows xp professional does not work to uncompress some files that have become compressed automatically

Hi I need urgent help to uncompress some of my files in drive d.Some of the files mostly audio and video files suddnly turned blue and automatically became compressed files.I have tried to uncompress them by opening property of root files and uncheck compress box by clicking advance but when I click apply and ok I find no difference in the compressed files their colour is still blue and property is same,that means system does not uncompress these files.I have also used command prompt but it does not work.Please help me to sort out this problem. Thank You Dr KK