Measure the resistance of the polyfuse with the multimeter, it should be a very low voltage, sub one ohm. To measure that set the meter to the lowest ohm setting (if it has multiple), then measure what you see if you short the testpins together, it might be something like 0.3 Ohm. Write that down, now measure between the pins of F3 (on the back near the power input). Obviously with nothing connected to the PI. Now you might measure something like say 0.7 Ohm, subtract the 0.3 Ohm, and you end up with an approximation of the resistance of F3 (0.4 Ohm).
Post it here.
Now turn on, and boot the PI, with a keyboard and mouse attached, but nothing else.
Set the multimeter to the lowest DC voltage setting.
Now measure the voltage across F3 (same points as before when measuring its resistance).
Post the result here too.
This will give us both an indication if the fuse is OK, but also an indication of whether the PI is drawing more current than normal.
You can also connect HDMI and see if the voltage across F3 increases, this is an indication that the HDMI is using current, it shouldn't (much).
In the end disconnect all, and measure again the resistance of F3, as described above, so see if it has changed, it should not.