Why did dell close your account for no reason My balance was zero and my credit limit was 4000?

This would be a question to ask DELL, not us.

Some companies may close accounts after some period of inactivity. If you had a zero balance and hadn't bought anything for some time, they may have just closed it because you didn't seem to be using it, so they closed it to tidy up their accounting system. If this is the reason, they'll probably be happy to reopen it for you if you call them.