Photoshop CS4 won't open

I've had PS CS4 for about 4 years. I use it every week or 2 weeks with no problems. Today I clicked on the icon and the splash screen with the developer's names comes up, it scrolls through a few startup operations until it reaches "Reading Preferences" and then it just stops, nothing else happens. I'm running Win 7 Home Premium. Nothing has been updated or changed since the last time I ran PS. Can anyone help me figure this out?

First thing I'd do is reboot and try again.
If that doesn't work, the preferences might have gotten corrupt.
You can restart Ps with Control + Alt + Shift immediately after double-clicking the .exe file and it will reset your preferences and hopefully open.
Of course, you'll need to go and change any Preferences back the way they were.

I rebooted several times with no change. I then tried to delete preferences with ctrl/alt/shift and it just wouldn't work. Finally I discovered that clicking on the pinned Ps icon in the taskbar at the bottom of the Win 7 screen won't work. When I did ctrl/alt/shift while clicking on Ps in the Start button I was able to delete the preferences and things were back to normal.

Glad it worked for you.