Try a different reading program.
If it is a nonDRM ebook you've got lots of choice.
CoolReader http://sourceforge.net/projects/crengine/ is really quick and lightweight for reading a single book,
and Calibre http://calibre-ebook.com/ is good too as a manager and reader.
If it is DRM you have less choice.
Sony Reader https://ebookstore.sony.com/download/ is the only one I know. It is designed to use with SOny devices, but can work standalone.
Overdrive works for library books but not for bought ones.