I have the same white / blank screen issue after trying to install either wp e-commerce or Ready! eCommerce plugins. Basically the back office disappears when you install or activate these plugins and the only way to get it back is to delete the entire folder from the plugins directory using FTP. With WP Ecommerce both the website front end and back office crashed but with Ready Ecommerce only the back office screens for Pages and Plugins / Pages / Appearance / Settings become inaccessible (I can still log in and see the Dashboard home page but little else).
My host assures me that the problem is not memory related and indeed I have Plesk server admin tool access and have double checked memory allocations for the domain name several times.
So I wonder if it is a conflict with another plugin? Here's what I have installed, with Theme 'Responsive' and a very basic 3 page website so far:
All in One SEO Pack
Contact Form 7
Custom Permalinks (number 1 suspect for conflict with WP Ecommerce)
Should I install using manual FTP rather than from within the WordPress Back Office? Or is there a simple step I am missing (change permissions of files/folders or chmod command or something) that is obvious to someone more technical?