crash after installation

If you have a white screen, you likely encountered a 500 Internal Server Error. That error should be logged. We need to know what error caused the white screen. Do you have access to php or web server error logs?

If not, you can try activating Gravity Forms again, but first, activate the default Twenty Eleven theme, and deactivate all other plugins. See if you can successfully activate Gravity Forms at that point. If you can, then activate plugins one at a time and see which one causes the white screen.

Also, be sure the plugin you uploaded was not corrupt by downloading a local copy again from the download page, and install via the wp-admin/plugins page.

Steve, to get back into your admin, use FTP to log in to your server and remove the whole Gravity Forms plugin. That will let you back in to the admin so we can see what happened.

I did see the error log you posted for a little while but did not see anything related to Gravity Forms specifically. A couple warnings and notices, which were inconsequential, but this one is most likely related to the problem:

Request exceeded the limit of 10 internal redirects due to probable configuration error

I would try disabling all other plugins first, then install Gravity Forms. If everything works OK, try enabling plugins one by one until everything goes blank. At that point you have found a problem. It could be a conflict with that specific plugin (which you can confirm by deactivating that plugin and enabling another one instead, to see if the screen still goes blank) or it could be a memory issue. You can find more troubleshooting tips for theme and plugin conflicts here http://rkt.gs/testing

It is either an "out of memory" issue, or a conflict with a specific plugin. When the screen goes blank like that, there should be a 500 Internal Server Error logged. We need to see what the error is to know what the problem that caused it was.