My applications keep getting deleted!

I've had my macbook for a couple of months now and recently my applications have been acting up. Some of them on the dock wont open up, and have a white question mark over them even though i have done NOTHING to delete them, or altered anything in anyway.

So far, my text edit and preview apps have been deleted but i restored them by downloading them again from the install disks using Pacifist, but now they are gone AGAIN along with my iPhoto and Photo Booth. I don't want to have to keep re-downloading my applications so what is wrong with my mac and why is everything going missing?

When you install these applications, do you actually move them into the Applications folder? Also, when you create shortcuts on the Dock, what process do you use to do so?

Sounds like you aren't installing your applications correctly. Like Cwa107 said you need to mount the .dmg file or whatever file it is and then drag the thing into your applications folder.

Then you can open the program from there, while it's open it should be down in your dock. Click and hold on the icon and you should see the white bubble box with "Keep in Dock" or something similar. From there you can move it around and rearrange it's location on the dock.

I'm pretty sure im installing my applications properly. I mount the files and i put them in the applications folder but my main concern is WHY they are dissapearing from my mac in the first place. All these programs are ones that came with my mac so why are they dissapearing all of the sudden?