You were selling mostly preowned car parts, yes? That's the best I could gather from a few of your feedbacks.
Something about your account was flagged as high risk. eBay generally doesn't give out details as they don't want people to try and circumvent their rules, so you probably won't get any more detail than what's in that message: high risk selling.
They mentioned "performance and activities." Was your performance impacted by buyer claims of non-receipt or a lot of return requests? If the answer to that is no, then it has to do with "activities" which could be anything from product to location to price to account info - there's really no way to guess when we can't see all of that.
Were you listing on the .com site or a different eBay site? You can go to the site where you listed and go through the help pages to contact customer service. Ask them if there is any way to appeal the restriction or if it's permanent.
Generally if there's a way to appeal they'll put that in the message, and the fact your message doesn't have that info it appears your restriction is permanent.
