What should I do to stop blender freezing on start-up, when its okay starting from a double click .blend file I was animating and asked blender to do a 15% render. It crashed. (2.73 with some add-ons activated)

Trying to re-launch Blender double click the Blender (windows7 start list) icon it showed a featureless grey screen and then freezes. (No splash screen)  (2.73  and 2.72b equally bad)

But if I double click a .blend file then 2.72b launches with old preferences and runs normally.

After using that method for a day I retried launching from the start menu.  This time 2.73 launches correctly and then freezes as soon as I try to do anything.
2.72b still goes immediately grey screen freeze.

I don't even know where I should be asking the question to try to find a solution.

W7 pro 64bit   Blender 2.73  and 2.72b  both 64 bit.  nvidea quadro   i7  -had been working noramally for last month, many many hours.
startup file can be messed up.

Open with a file that's ok, reload factory settings and save starup file.

If preferences (addons or anything) are messed up, do the same but open prefs and click save user settings.

If something's wrong in program data or manually added scripts/addons, explore C:\Users\ [userName] \AppData\Roaming\Blender Foundation\Blender and delete everything (or move).

After a crash, blender files could be corrupted. You can uninstall-reinstall blender to fix them.

If nothing helps, you can check your disks (all where windows, blender and .blend files are) from explorer RMB on the disk you want to check, properties, tools tab, check now. In the pop up, check automatic repair, uncheck search and fix defective sectors (or something like that, translating). This won't last long.

If this fails at fixing, try to check fix defective sectors but it'll take more time and for windows disk, you'll need to restart (and wait).