Problem with Lassos (Photoshop 7.0)

I recently got a new computer, and have been having problems with the polygonal and magnetic lassos. Whenever I use them, after a while my screen blinks and the the selection finishes against my will.

I use these tools frequently and this problem is a major cripple, basically making the lassos unusable. How do I remove the blinking? If I were to upgrade my Photoshop version, would it still blink?

Has no one had this problem? Is it just because my version is too outdated for you to have experienced it?