With a single click, my application opens

Dear All,
Hi, I am Oliver Ville. I have a minor issue with my mouse. Whenever I do a single click on one of my applications, the program just starts to open or load. I am using in a setup that once double clicked, that’s when the program should open.
I think that is the conventional setup.
How will I get the settings of my mouse back to normal? I am not that much technical when in terms of locating and troubleshooting where the issue is. As much as possible, I do not want to touch any settings, unless advised of course, by the experts. I am using a Windows XP machine and a Dell mouse.
Please help me resolve this mouse issue.
It keeps getting into my nerves every time.
Thanks.
