Hitting F5 only reloads the page, if it's cached it will load it from there.
Ctrl+F5 will force reload the page from the source site and overwrite what's in the cache. That often works and cures the problem.
However to really sort it requires getting rid of any old stuck cookies as well, the instructions above do that, clear any cached data and work much more regularly than a 'cache clear' on its own.
CT