You will need to removed both batteries, to get the camera to "reboot".
The 350D/XT has a separate date/time battery, in addition to the main rechargeable. The date/time battery is in a little drawer next to the rechargeable.
It's sort of like restarting your computer to clear RAM, to speed it up and resolve problems. After all, DSLRs are basically computers, too.
Do this:
1. turn off the camera.
2. remove both batteries (note: the date/time battery is shown on page 38 of your manual).
3. turn camera on
4. press the shutter release button once (note: it won't fire, this is just done to drain any remaining power in the camera)
5. turn off camera
6. reinstall batteries (note: wipe the contacts to be sure they are clean of finger oils, etc.)
6a. this might be a good time to replace the date/time battery, if that's never been done (life of these is about 5 years)
6b. if the main rechargeable is old, it might not be taking a proper charge either (life of these is about 400 recharge cycles)
7. turn on camera
8. check the date/time: if it needs to be reset, you got a proper reboot. If not, repeat above.
9. if repeating still doesn't give you a proper reboot, try leaving the batteries out for about an hour instead of pressing the shutter reelast button.
There are no guarantees this will work. But it's free and easy to try.
I would strongly suspect the rechargeable batteries if they are older. After a certain age and certain number of recharge cycles they tend to go bad and what you are seeing might be due to low power supply. It also can be a charger going bad. That's rarer, but does happen sometimes.
If you get the camera working again, don't forget to re-format that memory card in the camera. Formatting it elsewhere, as you say you've done, it might not work right until it's redone in-camera.
Sorry, can't recommend any repair people in your part of the world. This is the Canon USA website and forum. Maybe some other sites are a bit more international or closer to your home.
Hope this helps
***********
Alan Myers
San Jose, Calif., USA
"Walk softly and carry a big lens."
GEAR: 5DII, 7D(x2), 50D(x3), some other cameras, various lenses & accessories
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