in this case something is wrong with the software ..was damaged or issued in a way ..and I will recommend a full update of the firmware ..
Here is the site ..and I checked there is an update for it ..and all you have to do is to select the model (from the all list ) and the operation system and the firmware ..updates..Download them and connect the recorder with the data cable ...be sure the driver is installed if it has one for communication reason ..and run the update and follow instructions..
if the update do not work try to download the original firmware and just reinstall it ..without the update cause this kinda operations may be the cause in the first place ..
http://www.olympus.co.uk/consumer/2590_software.cfm?category=10&productgroup=0&product=442&os=7&result=If reinstalling the firmware will not do the job
than there is something fizically wrong with it ..and probably at the amplifier level cause it may record them well but not play them loud..