Sine source outputting wrong signal
Take a look at the time frame across the bottom of the chart.

It ranges from 0 to 1 microsecond.

Your signal generator is producing a 1kHz signal.

The chart is showing you 1/1000 of a single cycle of your sine wave.

Over that period, a sine wave looks like a straight line.   Over a short enough time period, everything looks like a straight line.

To see your sine wave, you need to extend the length of the analysis.

If you extend the time to 1 millisecond, you will see one full cycle out of your generator.

To see what your amplifier is doing, you probably need to see more cycles.  Say, 10 or 20 milliseconds.