download rar , i had the same probb.

Dude it must be in rar file, extract it(in some cases there is a .tar(rar file) extract it dem file will be in it extract in cstrike folder and rename it to 1.dem(or any catchy word and do write .dem at end) and then open cs > Viewdemo 1.dem

not it. Iv done it before. Now it says I need to open it with a program. And when i move the demo it deosn't show up in view demos.

It could be that the demo you are trying to view is from a previous CS protocol(minor updates that can sometime make demos incompatible with the current version of CS) or even version(major changes, such as CS 1.5 to CS 1.6) entirely...

If that is the case you'll need an external software program such as the coL Demo Player or SK Demo Player. You may need to update your .NET frameworks however to use these programs as they are more stophisticated than most.

If that isn't it the only thing I can think of is either the demo is or has become corrupted somehow or you are placing it in the improper directory to be played from.

Also one last thing, you could try using playdemo instead of viewdemo (sometimes this can solve indeterminent problems when attempting to watch a demo).