My system is playing too slow, a mezzo soprano sounds like a contralto! Any ideas please?

My system seems to be playing too slow, either when playing tracks from iTunes, or when attempting to convert vinyl records to digital tracks. The only common aspect to me is the computer, does anyone have any suggestions or ideas as to the source of the problem? For information, my PC is a relatively new one (about a year old) and the system is Windows 7, the record deck is an iTTUSB operating with the EZ Converter programme. My iPOd Touch continues to play at the correct speed. Help please?