What graphics card are you using? Sounds like you have your monitors connected via DVI cables as most cards only come with 1 HDMI port.
This is all based on the assumption that you are running a 64bit version of Windows 7.
If you have a nvidia card then I assume you are using the nvidia control panel to set up your displays. I have dual 560ti's in SLI and can run 2 monitors and my TV at the same time but I have it set up with 2 displays on one GPU and the other on my 2nd GPU.
I have not tried to connect all 3 to one GPU so I am not sure if it is possible to have 3 displays on one card.
Try connecting just one monitor and set it up using the nvidia or ATI control panel (or whatever ATI uses), then connect the tv and see if it is recognized. Then connect the other monitor and see if it is recognized. Then check the box to enable the TV and see what happens. Does the other monitor disappear?
Also go open up the Windows Control Panel >All Control Panel Items>Display>Screen Resolution and try setting things up there.
Most nvidia based cards cannot drive more than two displays at once unless SLI is being used.
If you want more than two displays you need a special version of an nividia card (zotac and galaxy make some), an SLI setup, or an AMD Radeon card. From what I understand Radeon cards are generally preferred because they can still hit the idle state when more than one display is hooked up whereas most nvidia cards run full blast at all times and thus use more power.