Most login problems stem from a problem with a web browser registering/storing/reading cookies. When you log into KH and check off the [I]remember me[/I] box a cookie is set on your computer. When you leave the forum and come back at another time, the forum looks for that cookie and automatically logs you in. If it can’t find the cookie or if the cookie is corrupt you will be prompted to log in again.
I forget how long the cookie is set to last on KH. I think it’s relatively short term (not years into the future). However, it should still remember you from one session to the next without making you log in each time you access the web site.
It sounds like you have tried clearing you cookies which is a good idea as it can remove any corrupt or stake KH cookies (from our older forum perhaps). You might also want to make sure you don’t have any software installed or browser plugins that are blocking cookies from being set. When cookies first came out many people were paranoid of them. Many system/ant-virus software exists that includes cookie blocking features. Browsers can also be set to no longer accept cookies, so you might want to check that you have cookies enabled.
Another possibility is your browser is having some trouble handling cookies. You may want to try reinstalling your browser or try using another browser if you have one installed on your computer. You can also try installing a different browser such as Firefox.
I hope some of these suggestions help you get the issue resolved.