Is it your account you cannot access?  Have you tried clicking on your feedback score, or View Listings top left of your post above.

Or are you having issues actually listing an item?

Is it the same today?

If an account is not used for 60 days it can deactivate,  you may need to contact Customer Services, as someone suddenly trying to sell on a dormant account may be a sign of the account being hacked.  They may need some verification from you that you are the genuine owner.

Contact CS with the link below for a Call Back option.  Try at 8 a.m. on weekdays as there's more chance of Dublin answering. It's a Call Back option, so you'll hear if it's Ireland calling!

https://www.ebay.co.uk/help/eua?id=5190

@41glassman