Busy message on viewfinder

musiccankill

Hello!
I am new to your forum and I decided to ask a question here to see if we can find a solution for my problem and maybe others with the same problem too!
My T2i camera I bought used shows a busy message on the viewfinder. The LCD is faulty so I cannot see if the busy message is there too, but I have no reason to believe that it won't be. Most of the time I power it on it doesn't allow me to take pictures or do anything else. I have checked with the card from my 600D (class 10) which works flawlessly on the 600D, with no luck on the T2i. When I pull the card out it focuses, releases the shutter and shows the picture taken as normal.
And here comes the mystery part...when I connect the AV (not HDMI. Haven't tried with an HDMI) cable ,no matter if I connect the cable to a tv or to anything at all, the camera returns to working condition and saves on all cards with no busy or other error messages at all! I found this out because the LCD is faulty (doesn't show anything but black screen. Only backlight works ok) and I wanted to see if it will show the menu on the external screen which it does perfectly!!
I have tried to find out what's going on with no luck. The main board seems ok and corrosion/watermark free. The LCD has watermarks so I assume that's why it doesn't work. I have ordered a new one to change it.
There are days and times that it works without the AV cable, but most times it refuses to work unless I have the AV cable connected!
I have tried to refresh the firmware and I have installed MagicLantern to check the internal temperatures, which are normal (max 40C at over an hour powered on and shooting)!
I would like to hear your thoughts on what it may have!
Thanks a lot!