New Installation not work / White screen.../ iMAC

Question

Hello , i hv this iMac  : iMac 12,2, Quad Core i7 , 3.4 Ghz , 8 MB Ram , SMC Version 1.72f2 , HDD 500 GB , Serialnumber xxHJW.
I make a new installation snow leopard with the gray DVD ( no backup because all my datas on a server ) include all updates . Yosemite runs one time.
After reboot i see white screen . Nothing more. I reboot . Check with safe mode and a lot more… nothing happened .
Than i put out the hard disk and format ( i take this how to Mac OS X 10.6 Snow Leopard: Löschen und Installieren - Apple Support )
them on my macbook . After I take it back in the iMac . I Test Internet Recovery (CMD + R ) , boot from DVD / USB boot Stick Maverick...
Nothing , every time is see the apple + rotating circle , after than a white screen and nothing happened. I check them with a new
harddisk . The same…
I check   -->>  Apple Hardware Test ( ALT + D )  --..>>  all ok , no errors
ALT +CMD+ P+R , ALT +CMD +N +V --> i do…
I installed WIndows 7 Professionell --->>  all ok , no errors
I make a USB Start Stick for maverick , when i start with them i see a blue screen .
I do a --> OS X Recovery Disk Assistant v1.0   from here -->> OS X Recovery Disk Assistant v1.0  -->>  nothing happend --> apple symbol , rotating circle,
after than white screen …
Any person has an idea ??
Best regards,
Peter
PS Sorry about my bad english

Answer 1

hi rkaufmann , i check with there serial number on the apple site :
iMac (27-inch, Mid 2011)
Seriennummer:
xxxxxx9DHJW
best regards