CS2Photoshop-Brush, clone stamp and eraser tools not functioning

I'm working on a brand new Hp with Windows XP Professional. I have 1GB RAM, 158GB of free space, my graphics card is Intel High Definition Media Accelerator 900.
I purchased an educational version of CS2 suite through journeyed.com in August. Photoshop seemed to work fine, then one day when I had to erase something it wouldn't work, along with the clone stamp tool and brush tool. They seem to work only about 1/10 times of starting up Photoshop. These are tools I use regularly and rely on to finish my work so it's essential that they work everytime I start up photoshop. I've tired shutting down my computer and uninstalling the suite completely and reinstalling it. I'm fed up and don't know what to do. Please help me.

You know that rectangular thingie with the blue bar on top and the feather underneath?
Three sections up from the bottom there's a section that has a teeny little black box on top of a teenie little white box?
Click on it.
When you want to erase make sure the big boxes have the white one on the top when you want to erase.
I have a hunch this may solve some of your other problems. Maybe not.

Move the pen away from your tablet.

As Michael says, having the pen near the tablet can play havoc with PS when using your mouse as both devices try to take control of your cursor.

If this turns out not to be the cause, try resetting the Preferences file as per the FAQs.