sound problems

i'm working with a dell xps r350 pentium II and windows 98 and suddenly i've lost my sound. i can insert a cd in the tower and no problem ... i can hear everything. it's just that any of the sound from anywhere else, i.e downloads are mute. i must have done something but i don't know what it is.
also, one last thing i'm finding many of the pic i download from various sites are coming up with a red x in the corner of where the image should be. not all but many and varies from site to site. could this be related to the sound problem?
thanks.

 

start - programs - accessories - entertainment - volume control

make sure everything in there is turned all the way up.

 

o and the pics show up with red x's because your computer doesn't know how to display them. That could be any number of problems, but the most likely one is that it doesn't know the format.

 

many thanks for the tip but i did that and everything is on and at full volume. still no sound except from my cd's.