Yikes! Help! What's going on with my 5D mk3?

I always download my photos by plugging in my camera, I've done it like this for years without a problem. This morning I first downloaded off the 7D and then plugged the 5D in and it did nothing. I unplugged it and tried to turn it on and it wont. Then I noticed the red light on the lower right hand side flashing even though the actual camera was turned off.
I've removed the battery for now and thought I'd ask here if anyone knows what's going on with it.

Whippeticious wrote in post #16304384
I always download my photos by plugging in my camera, I've done it like this for years without a problem. This morning I first downloaded off the 7D and then plugged the 5D in and it did nothing. I unplugged it and tried to turn it on and it wont. Then I noticed the red light on the lower right hand side flashing even though the actual camera was turned off.
I've removed the battery for now and thought I'd ask here if anyone knows what's going on with it.

Sounds like its having a problem writing to the card.

You might want to take it out and check for pin problems.

I haven't removed the card since I first put it in at purchase about 18 months ago. I dont understand why it would have pin problems.

Whippeticious wrote in post #16304400
I haven't removed the card since I first put it in at purchase about 18 months ago. I dont understand why it would have pin problems.

Or maybe it needs to be formatted? Or it got jarred loose?

The flashing red light indicates writing to the card (unless that model has other uses for that light than I'm familiar with).

Hmmmmm I've put the battery back in and once again the red light started flashing even though the camera was turned off. I tried switching it back on and the red light flashed a couple more times but the camera remains deady bones. Nothing...............

Have you removed the card yet?

Yep, just tried that, took it out, put it back, still nothing.

My other suggestion was that it needs to be formatted.

but if I formatted the card wouldn't I lose all the photos that are on there? Also, I cannot do anything right now if the camera wont turn on, and that's the problem I'm having at the moment.

if the camera won't turn on, remove the lens and see if it will turn on. Is the lens a large telephoto ?

I'm gonna go out on a limb here and suggest that maybe your battery is dead? Charge it a little bit and try again.

aaah! I've just tried swapping the 7D battery into this camera and it turns on! Phew! so it seems there's a problem with the battery. Strange, I recharged it yesterday and it seemed fine. For now I'm just relieved the camera's working.

The red light may just indicate, busy, which would be signal in/out of the usb. It may even say busy if you look through the viewfinder and try to get the camera to do something else.

Have you rebooted the computer? It sounds like fast switching of the camera has tripped up the computers recognizing the device was changed. If it still doesn't work on reboot then I'd download or get out the disk for the Canon software and reinstall the drivers.

Before you format the card I'd make the effort to try and download the images from the camera via a card reader (which you will likely find to be much much faster than plugging the camera into the PC).

Also if you can put the battery in the camera hit the play button and view the photos, then they likely aren't corrupt.

You can format a card and generally with special software recover the lost data so long as you do not write over the deleted information.

Whippeticious wrote in post #16304488
aaah! I've just tried swapping the 7D battery into this camera and it turns on! Phew! so it seems there's a problem with the battery. Strange, I recharged it yesterday and it seemed fine. For now I'm just relieved the camera's working.

Good to hear.

HiepBuiPhotography wrote in post #16304487
I'm gonna go out on a limb here and suggest that maybe your battery is dead? Charge it a little bit and try again.

You were writing at the same time as I discovered the problem. I fully charged that battery yesterday afternoon, after I'd taken all the photos as I noticed it was getting low. When batteries die, is it usually completely sudden like this seems to have done?