1.Type in UCS then W for world, that should set you back to normal
you can use the UCS command to rotate the crosshairs anyway you need, if you are in plan view you would rotate it by the Z-axis such as UCS Z <enter your angle here> use negative numbers to rotate clockwise, or positive numbers for counter-clockwise.
2. Command: _ucs
and choose W (World) to return to default set.
If you want the axis rotated after _ucs you choose Z and enter the rotation angle you want
3. If UCS doesn't match crosshair, you may have a rotated "snap" angle. Try SNAP>>Rotate>>0
If you want UCS aligned with the screem, use the PLAN command.
4. If I fully understand you, then the following steps should help.
Activate (double click into) the viewport which you wish to rotate.
Type UCS {enter}
Type OB (for object) {enter}
Select a line which you wish to be horizontal on screen. Note that the end of the line you select will be closest to the UCS origin.
Your crosshair in the viewport will now be aligned with the object you selected.
Now type PLAN {enter}
C (for Current UCS) {enter}
Your viewport view should now be rotated. Post back if you have a problem.