Ok, I've been using Blender 2.73 for a while now.  I'd been following tutorials and making a lot of progress thanks to you guys in this forum.  Suddenly, I just noticed that whenever I add a new mesh from the Create panel, like a box, or cylinder, or whatever it may be, I no longer have access to the parameters to adjust that new mesh.  All the parameters that are usually on the left hand side of the UI are gray, and I can't change any of them.  I already shut down and restarted several times, but it makes not difference.  This just started to happen.  So I add a cylinder to the scene, but I can't change the number of vertices, radius, or Cap Fill Type anymore!  What gives?  I don't think I pressed anything I shouldn't have, and they were all working fine just yesterday!

This sucks.  Nothing I do fixes the problem.  Do I have to reinstall Blender all over again to fix this?

Ok, this is officially the strangest thing ever.  I actually went and reinstalled Blender 2.73a again, but the same problem happens.  I can't change any of the parameters in new objects I create from Add Mesh.  However, if I enter the edit mode of an object, any object, I can then add a new mesh and it WILL allow me to adjust the parameters on that object!  WTF?  Is this not the weirdest thing ever?  I can't help but think I pressed a hotkey to make this a preference, but what?  This is one thing I hate in Blender.  It's so easy to screw things up beyond repair, it seems.  How can I reset everything back to factory state, so to speak?

I assume you are talking about the Add Primitives > Tool Shelf properties?  This is likely caused by one or more addons you may have installed, conflicting with the operator properties.  I can't say which addons might be the problem here, but usually when something like this happens, that's the issue.  Unfortunately, there's not a quick fix to this.  You could try launching Blender from the command/console prompt, and view which errors are being reported, if any.

You can try resetting Blender to default "Factory State" by going to File > Load Factory Settings.  I doubt this will help, but worth a try.  You say you re-installed Blender again, and it did not help.  It sounds like you may have simply installed Blender over the existing copy, which would not erase or reconfigure certain issues.  You need to UN-install Blender first.  Go to your Blender Foundation folder, and double-click the Uninstall icon of the version you currently have installed.  It will prompt you through the uninstall of the current software version.  Then, once the software is completely uninstalled, go ahead and re-install it again, from a fresh executable file.

This should work to bring Blender back to an original software state, and remove any conflicts or addon errors which may have been occurring.  Once you verify the problem is solved, go ahead and start initiating some addons again, but be mindful of any conflicts or error messages you might see in the User Preferences > Addons tab.

Ok, well that worked!  You're right, I just installed it over the old one, and that did nothing.  I tried the load factory thing, and that did nothing.  Nothing worked until I uninstalled the software, and installed it fresh again.  Bad part is that all my customizations are gone, and addons need to be reloaded now.  But at least the software is running like it should again.  Thanks for the fast reply, luxxeon!

Just an FYI I use to have issues when I installed Blender to its default location in C:Program FilesBlender seemed that depending the particular add-on I might be using had to write back to the install directory and due to Windows UAC user account controls thinks would just not run as smooth as I would have preferred. I started installing Blender to the root of my C drive and all the little annoyances stopped and Blender has run so much smoother with hardly any crashes of freeze up just possible trick when working with Windows Vista thru Windows 8.1

Oh wow!  I had not thought of that, Lobo3433!  Good idea.  You're probably right about that, and I'll bet you dollars to donuts that's what was going on.  Because if it was just any ol conflict, then why didn't it happen sooner?  I'll bet it was a Windoze permissions thing with one or more of the addons I had installed, and that caused the issue later on. Thanks for that tip.

My pleasure I have started to install many of my 3D apps outside of the default Programs or Programs (x86) and have found them to run smoother with less crashes like Hexagon and Silo which dont have add on's per say but installing them to the root of the drive has cured many of the crash issues and such. I got the idea when even Poser Pro started installing content to my document folder instead of the old default program files folder. Granted with Blender you can also run it from a zip file that is not even actually installed. 

Good Luck 

Running it out of the folder that comes in the .zip download is how I use it now. I keep two or three versions around in case anything breaks in one of the updates. But I also like to check out the new stuff as it comes along. No problems running it that way, although sometimes I have to manually copy prefs or copy over certain add-ons/plugins to multiple blender version folders when I find I'm missing something.

I agree I have one version installed and keep several previous version that I run from zip as well