Hello,
I have been working on one image for about 4 days and the size of the file is 25,148 KB. Last time I worked on that file I saved it as usual, then tried to shut the computer off which took around one hour because one other program was not processing. When I came back the next morning, the file was a blank sheet even though it still has the same size as the day before. Is it possible to get the image back? I am using the latest version of Inkscape (0.91).

Thank you very much for answering in advance.

Welcome aboard!

It's actually a good sign that it opens up, and has the same size meaning it isn't damaged.
My guess the rendering fails on your pc's power. 24 MB for an svg is quite large, especially if there are no embedded raster images involved.
I'd ask someone if they can open it and then remove unused defs/cleanup document right after and save again -maybe that would help reducing the file size a bit.
(For example gradients are stored that way.)

If that doesn't work then a brute-force solution would be splitting the file somewhere by using a notepad.

Due to a bug when closing Inkscape while the file is still being written, there's also the option that the file hasn't been written completely.

To check for this, open the file with a text editor, and look if it ends with </svg>. If it doesn't, it's broken, and you'll need to close all open tags manually to make it show up as good as is possible again (or upload the file somewhere and post a link here, so that others can try to fix the file).