pblm in boot after downgrade firmware of fortigate 300c

DEAR Freind , After i had restored the config-file in my new fortigate  ( with forti-os 5.2.10) , all port( in the fortiASIC powered pannel ) are down ( led off ) , i can't connect to my newfortigate via phisical port ! , i have dowgrade to 4.3.8 ( this version is the current of my other HA - fortigate  ) but i have other problems , i cant acces to my web based manager and command line interface , i use the consol port to get more information of this problem but have wrong text code . now , when i try to upgrade my new fortigate with fortiexplorer i have this message : CAN'T UPLOAD FIRMAWARE FILE ! (-40) . FAROUK .