It's strange that other OS's seem to work fine for you with this board but not Windows 7. Now that you've had several incidences of improper shutdowns, these will definitely impact your system integrity so was the new Windows installation performed from scratch on a freshly partitioned and reformatted HDD (strongly recommended) or was it just an 'over the top' reinstallation?
If you try the setup on a blank HDD (if necessary by disconnecting the existing one(s) and using a spare), as long as you perform the installation in the correct order ie Windows DVD, Windows live updates over Internet, Intel chipset drivers, remaining Intel provided motherboard drivers and then discrete graphics card/other hardware drivers, I'd be surprised if it still plays up. Note that it's important to remove other partitions and OS's and any other 'complications' from the system before testing. Once you've re-established a reliable system (as it was before 'the day' you referred to, then you can go and customise away again and monitor the system for reliability changes or freezing incrementally during each step of those customisations.
Given the other post you referred to indicates code 51 may be associated with a failure to initiate PCI devices, I suggest you shut down and remove the discrete graphics card and simplify your system as much as possible before attempting any BIOS upgrades.