In computer, highlighting malfunctioning?

Recently my highlighting (that is, when you hold down the right mouse and drag the cursor over a text, for example for cut and pasting) has been malfunctioning -- the selected text will only stay highlighted about 20% of the time. Also, clicking on menus is also malfunctioning in the same way. Finally, my calculator sometimes doubles the digits I click on (I click 2, it gives me 22.) Short of re-installing the operating system, is there anything I can do about this? I have a Pentium 3Ghz computer, RAM 2GB, 32 bit OS, running Windows 7. The highlighting problem also exists in other applications besides Word, such as the text boxes in an email.