How many messages and folders in your inbox?
You may just have so many messages that you are using up your system resources when you open OE.
Next, which version of OE?
If version 6, which video card?
And, have you tried updating the video driver?
If OE 6, and the video driver is more than 2 years old, you may have a compatibility problem.
21MB of free hard drive is NOT much for Windows, unless the page file is on a separate drive.
Even with 512MB of RAM, you need a minimum of 500MB free hard drive space for the page file.
Personally, I would prefer to have 1GB or more available..
The more I think about this, your problem is that you are running out of resources.
You need to purge your inbox and message folders.
Then, clean up the C: drive to create more free space.
Chas