I tried to install Ubuntu multiple times yesterday with no avail. I have a brand-new 1.5TB HDD and had 870GB left on it.
During the first step of installation (resizing partition using 100GB) I got this error:

Ubiquity:5851): Gtk-CRITICAL **: gtk_widget_draw: assertion '!widget->priv->alloc_needed' failed

I then turned my PC off and booted back into windows to see there was 100GB missing. I looked at my partitions within windows AND Ubuntu 'try' mode. There's no partitions and Ubuntu didn't install... I really would like to get my 100GB back, can anyone help?