Help With Quaternions

How come this code gives me a blank screen:

Code:

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'Yes everything is initialized
Dim Quat As D3DQUATERNION
Dim Mat as D3DMATRIX
D3DXQuaternionIdentity Quat
D3DXMatrixRotationQuaternion Mat, Quat
D3DDevice.SetTransform D3DTS_WORLD, Mat
'Draw mesh

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When this one works perfectly?:

Code:

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Dim Mat as D3DMATRIX
D3DXMatrixIdentity Mat
D3DDevice.SetTransform D3DTS_WORLD, Mat

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When they should do the same thing!