Check to see if the CTRL key is not jammed down or the Properties key is not stuck.
Just tap the keys lightly to see that they are free and then give it a try.
Go into the control panel and check mouse options:
First panel itself has an option which says "Switch primary and secondary buttons" makes sure the box there is unchecked.
Sometimes, setting it, and resetting it, rewrites the setting to the file in Windows, because the file may have gotten replaced...so ticking and unticking and reticking will sometimes fix it....hitting "apply" or "okay" each time.