After finishing plowing,fields number 15 and returning to the farm,when I go to the marker the window is showing ,that I can start another mission and here the problem begins because they are blocking all the keys do not even have an arrow (the mouse does not react) there is a sound but you can not approve it start mission .
Open the Console by pressing "^". You should have a mouse again and be able to click the Start Mission Button.
the marking on the key that opens the console will depend on your keyboard layout and region.
often its either the key directly left of the 1 key and above the TAB key.
else one of the keys right of the "L" key (QWERTY layout) between L and the large enter/return key.
e.g. for me with a UK keyboard its the key that is left of 1 directly above tab, with `¬¦ on it.