Op Amp Integrator not working with DC Source
Upon initialization, MultiSim attempts to perform a DC balance. Since for DC a capacitor is the equivalent of an open circuit, that's what you get.

Instead, replace V1 with a step function, with the output at 0 for t = 0, and an output of 1 for t > 0. Alternatively, replace V1 with an offset square wave with amplitude 0.5 and a 0.5 offset - that is swinging from 0 to 1. Make the frequency 1/1000 Hz, and as long as you're only interested in t &lt; 500 you'll be fine.