I have a canon eos 600d camera on the Cld screen there is a little white square in the middle how do I remove it please

SOURCE: Canon EOS 20D SLR CAMERA LENS - ERROR 01 ON SCREEN

Clean the contacts between the lens and the camera.

SOURCE: Canon PowerShot S2 IS Digital//Black screen HELPPPP????????

go there and you'll see you're not alone !
S2 IS Question: black screen in S1IS canon camera - DigitalCamera-HQ

SOURCE: CANON POWERSHOT S2 IS 5 MEGA PIXELS

I bought mine 2 1/2 yrs ago too. Found this solution on this site and tried it. It worked perfectly.
Turn to TV mode, set the exposure to 15 seconds by pushing the little "arrow dial" until you have 15"
Push the button to take the picture.
Wait 7 seconds from when you push the button, then turn over and open the battery door while it is "taking the picture."
Close the battery door and turn back on. 
I did this three times and the last time, it worked and the iris became unstuck.
Then I took a million pictures to get the iris moving.
Good luck!

SOURCE: Vivitar 3200 Flashgun and Canon EOS 400D

Using Vivitar 3200A flash gun on a DSLR is risky for the following reason. The trigger voltage of a DSLR at flash hot shoe that takes it to its TTL (through the lens) circuit is less than 10 volts, it is about 6 to 8 volts in the recent DSLRs. The trigger voltage generated by Vivitar 3200A at full charge flashing is around 180 volts (max). That is a fatal dose for a sensitive DSLR TTL circuit. This high voltage flash gun will work endlessly, the only damage is to the TTL flash circuit. When you attach a TTL flash to the DSLR after using Vivitar 3200A for sometime, your TTL flash will not communicate with your camera. It will be just another ordinary flash without any auto functions. There is a Wein adapter that you can fix b/w your cameral hot shoe and the vivitar flash gun that is said to reduce the trigger voltage that passes into the camera. Try it if you get it. Without this gadget it is better not to use non recommended and non TTL flashes on latest DSLRs.

SOURCE: EOS 600D I can not take a picture

Did you take all the typical steps? Taking out memory card and re inserting same with battery. Try making sure lens is properly attatched.