Keep the PC further away from the AC. So, it is closer to room temperature. Rather than below room temp from the AC blast.
The AC should be dehumidifying your air. Are you just depending on those crappy inserts they give you to seal the sides of the window? Sealing it properly will reduce humidity, keep bugs out and drop your power bill.
I cover the sides of the window frame with 2" foam insulation board. Any styrofoam board will do. I just went with this to maximize insulation. Even a couple layers of aluminum foil will do in a pinch. But it won't hold up more than a year and may be a bit noisy.
Then I seal around the board with aluminum duct tape. Regular will work too. I work this carefully so the board is sealed to the window...