Is it a case where you have to take the job because you need the money? If so, fair enough, but always remember 'have to take this job today' doesn't imply 'have to stay in it indefinitely'. Go ahead and start work in the open office, but in the meantime put out feelers, be quietly looking for a job that will give you a private office or let you work at home. The best situation in which to be looking for a job with your preferred conditions is one where you aren't desperate to find something quickly.