Cubase 6 dropouts and crackles but NO Asio or cpu overload

First sorry for my english…

I am having very serious problems with cubase 6 x64, I was using it without problems until last month on windows 7 x32, now I changed to windows 7 x 64 and it has been giving me cracklings and dropouts since I changed windows, I am using the same hardware setting as always:

yamaha N12 mixer,
Pc with a motherboard ECS Black Series P55H-A,
8 Gb of Ram
i7 Processor
Windows 7 x64
Video card Gforce 9800GTX+

it is giving me cracklings and very short but frequent audio dropouts , it does not maters if I play several audio tracks or just one plain audio track with no fx on it, is the same, the asio and disk meters in the performance tab are not moving, even in the dropouts nothing moves or gives spikes, there is NO overloads, in windows the cpu and ram usage are fairly low when this happens. the play line moves smoothly, nothing visualy jumps or lag, I have done, evrything, I update to Cubase_6.0.7_Update, I downloaded several n12 drivers, last I downloaded driver win_tools_for_n_v273x64 for n12 and that’s the one I’m using now that lets me sync the mixer to cubase for remote cotrol, I desable the mackie control , I installed my chipset drivers again, I have set the audio buffer to the minimun and to the highest values and nothing ever changes, I have set it to 256 default, 128 and 512, nothing changes, I desabled the internal soundcard on the motherboard, i set the audio prioryty in cubase to boost, multi procesing and back to normal, nothing, I change the asio driver on windows to Legacy, nothing, I disconect the ethernet cable, the antivirus and antispybot, change the firewire cable, change firewire inputs, nothing helps.

The wierd thing is that the crackels and dropouts ocur just when cubase is active, if Cubase is closed I can play audios on internet or windows media without a problem, when I start cubase everything start to give me crackles and dropouts inside and outside cubase, even the windows media, but ONLY if I use it while cubase is open.When I export audio from cubase the audio does not contain any glithches thanks God, is very clean, I usually fix my problems by myself but here I am trully lost.

I am using the same hardware as last month when everything used to work fine.
Please help, I have a client in my back and I cannot work with this problem.Tha nks, please help