How are the monitors connected? What gpu? For eyefinity you really need to connect your 3rd monitor via displayport 'ACTIVE' adapter. There's one person in here that claims to have gotten eyefinity to work with passive adapters, but no word on how he did it. So until I find a way with passive adapters, I will recommend active.
A list of approved dongles in this link;http://support.amd.com/us/eyefinity/Pages/eyefinity-dongles.aspx
Worth a read is this 'how to' guide by hugostiglitz;http://www.tomshardware.com/forum/344343-33-eyefinity-setup-guide