Why can't I target the reaper?

I'm fighting Geth, and I'm at the part where I have a targeting device and I have to 'target the reaper' All that happens is after a few seconds the reaper shoots me, I die. When I try and fire the device, all I get is a sort of impotent clicking noise, nothing happens. I've retried this 10 second 'mission' over and over, but I can't work out what to do, I always just get shot and die. What am I doing wrong?

Solution 1:

It takes a good cycle of dodging the beams before the targeting laser comes "online." You'll know because there's a little screen off the right hand side of the targeting laser. If you can't see this screen, just dodge until you can.

If you're having problems after it comes online, check this question:

How do I beat the Reaper on Rannoch?