Shields don't regenerate in single or multiplayer.
My shields don't renegerate at all in single player, making the game impossible to play. They only start regenerate when I set the difficulty to narrative or casual, which sucks out all the challenge and fun. I'm watching youtube playthroughs on insanity and hardcore, and other people don't have this bug - their shields regenerate normally and mine don't.
My shields also don't regenerate in multiplayer at all if I'm hosting.
I purchased ME3 several days ago and have all the free DLC packs installed, if that's of any help. Please advise.
I don't know if this applies to you or not because AFAIK the game's default settings cap your FPS at 62 which should prevent this from happening, but Caratinoid's thread on BSN suggests that extremely high frame rates will slow and even prevent shield regeneration, amongst other things. But of course that's referring to extremely, absurdly high frame rates, so unless you dropped thousands of dollars on a bleeding-edge rig I wouldn't worry about that.
Otherwise, have you tried the repair install option?