Unless it is a glitch, usually the message privileges are taken away for breaking the rules.
If you have not contacted any potential customers, without them contacting you first, it may be a glitch in which case you will have to email Etsy and wait.
If you have contacted potential customers, who have not contacted you first, then you have been banned for spamming which is illegal in most countries.
Those are the main two reasons why you would not be able to send messages.
If it is the 2nd, then there is no time limit for when the message privileges are returned to you and there would be no point wasting your time and effort emailing. Some sellers have reported their ability to send messages again after a few weeks following a ban, others still did not get them back after a couple of months so I assume it depends on the seriousness of the rule breaking involved.
