i have a Canon 350D modified for shooting IR.
it was fine until this morning, when i switched it on, it just wouln't turn on. i tried changing batteries and so on but no luck. i've no idea what's wrong with it, but what freaks me out the most is it is probably warranty voided since i opened it up to remove its hot mirror.

by the way im in Montreal, Canada. does anyone know where i should send it to fix? (and how much is fixing cost?)

Try removing the lens and cleaning the contacts in the battery compartment. Canon will fix it with pleasure, but they will charge if you don't have the warranty.