1. We've had some reports of issues with the YITH Ajax Navigation plugin - I would disable that and see if that fixes the widgets (i.e. they now expand). Simply disabling and re-enabling seems to work at times too.
2. General low memory which causes the widgets to also not expand. I'd disable: 2x Retina, YITH Ajax Navigation and any others you don't need. Keep disabling until the widget area expands. This has worked every time for me.
So, If it is a memory issue, you can increase the available memory by adding a line to wp-config - see - http://docs.woothemes.com/document/increasing-the-wordpress-memory-limit/
Once
added, try enabling the disabled plugins again one by one. A better
long term solution would be to look at hosting more suited for
WooCommerce - SiteGround are excellent.