PC not detecting my Hard Drive. (Not sure if placed in correct category.)

My PC is not detecting my HDD, I just built a PC with a low budget I bought a M4A785TD-M EVO a Phenom II X2 550 3.10GHz a ASUS ATI RADEON HD 7770 and 2 case fans I'm using the heatsink provided with my CPU and I have a Barracuda 500GB and 4GB of DDR3 RAM kingston everything is completely new I unboxed and installed everything I installed Win 7 64-bit Ultimate SP1 I had all drivers correctly installed and up to date and everything was working fine I always ran full PC checks with AVG and I monitored my GPU speed and temp with ASUS Tweak, I used the windows RAM test and found no problems and checked the HDD for bad sectors and it diagnosed perfect state I monitored my PC temp with HWZ CPUID monior and had 0% of disk fragmentation that was a few weeks ago, but then I downloaded Don't Starve and played for 2-3 hours when I was playing all temps were normal and the PC made no strange noises or anything out of order and all of a sudden the computer showed BSoD and then I waited until it dumped the memory into the disk and restarted the PC, then the message Bootloader is missing press Alt+Ctrl+Del to reboot I knew this was due either because the windows files were corrupted or the HDD was failing the I restarted and inserted the Win 7 Intsall disk and selected repair it said that there were no OS in the PC the I restarted went into the BIOS menu and the Installed Hard Drive DIsks was empty it just showed SATA1: No device, when previously it showed the model of my HDD I checked that everything in the BIOS were unchanged and that the Boot priority was correct everything was just fine, I checked the wiring was correct, I disconnected all the fans just to hear if the HDD was making any noise and the only noise was the usual noise it makes when running correctly I layed my hand over it to feel any vibrations and see If it was working it felt pretty normal, luckily I had another HDD with Win 7 x64 Ulti also installed I replaced my HDD with it and it worked just fine with nothing unusual so I knew the PSU wasn't the problem, both are the same model of 500GB Barracuda. Somebody please help me!!
And please don't be too harsh with me because of my english....