Can't start my W7 in AHCI mode

Notebook Clevo D901-c / W7 installed from beginning with sata set to AHCI. If i select restart, than it will restart normally. If have to Switch off instead of "Restart", than in the next restarting job session it'll hang on after ahci post message. Than , only procedure i have to solve this issue is: must restart and change bios to IDE restart it and wait for blue error screen, and finally while restarting go into bios and re select back to ahci. Start normally and select restart normally. When is running normally, if I check registry, msahci "start" service is already set to "0" so i don't know what else could do for . How can i solve it? Just for better explain, let's immagine that windows is running fine with BIOS in AHCI mode.

So if i have to "restart" my pc, than it will restart without any problem at all!!But if i select "Stop" instead of restart (switch off) the system, than in the next restart it will hang on blinking white little line after starting ahci post. Than the only way to get out from this freezing is: 1)force pc stop. 2) restart and go into BIOS to set sata mode to "normal" (IDE). 3) save bios and pc restart normally until the 4 coloured windows dot will appear. 4) at this point pc will stop due to blue error screen (that's normal of course because OS have been installed in ahci mode from beginning) so pc will attempt to stop due to blue screen and restart automatically. 5) while restarting go into bios again and set back sata mode to "AHCI" and restart.

At the end, will follow restart procedure and my notebook is capable to get W7 alive with original sata bios settings to "AHCI" and it run perfectly without problems. If now i get a look into registry looking for "msahci" than i can see it is already set to "0". So apparently nothing seems to be wrong and of course windows run very well. I can restart it without problems as many times as i want.

But.... is i'll select "Switch-off" than will have to follow above described steps in order to get it back alive.

I've check this happening with two different type of devices: Toshiba 240 Gb HDD and Corsair 240 Gb SSD. So, for both i have same reactions, same issues. I made a test also installing W7 on normal hdd with bios sata set to IDE from beginning and no one issue arised. Of course would like use AHCI for ssd one so that's my path on which i've found these troubles.

Notebook is updated to latest bios and all that stuff... i personally think that something goes wrong into W7 recognization of sata settings after complete switch off, but i'm not so expert to realize how could solve this issue.

Many thank's

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