This sounds like your cookies and temporary internet files could do with a clear out.
To clear cookies in Internet Explorer;
Tools > Internet Options > General Tab (should already be open on this).
Click 'Delete Cookies' & 'Delete Files' (If you haven't done this for some time, it may take a while to delete). Close browser and re-open.
If you need cookie clearing instructions for other browsers please let me know.
When logging-in ensure that
Minutes to stay logged in is set to 60.
Please let us know if that has solved your problem.
