There have been no reports on not being able to bid today, so it may well be the seller has blocks in place, and if they're not answering you they may well have blocked your messages too.
Have you had two or more unpaid item cases in the last 12 months ? This will block your bidding from the majority of sellers for 12 months.
Or, if you've had a recent break from buying you may have an in initial limit of the number of bids you can place, until you once again prove you are a reliable buyer paying for items promptly.
Buying Buy it Now items with immediate payment will help in the meantime.
