Unity will not start up......HELP!

I am running 2.6.1 on Vista. It has ran fine till 2 days ago, now it will not start.

Have you tried uninstalling and reinstalling Unity? I've had this problem when Unity crashes importing something, then again when it restarts, reloads the project, reimports the same object, and crashes again. You could also try moving the folder containing your project somewhere else so it can't find it on restart.

This happened with me with photoshop. n matter how many times I installed and unistalled it. It began to start up but after a few seconds it stopped and the process ended. I installed it on my memory stick and tried it on a different on a different computer and it worked. So I had to buy a different version of photoshop (I bought CS4) and then it worked on my computer. I suggest you upgrade to unity3.3. A few weeks later I reinstalled my OS and Photoshop CS5 was working again.