Since this is the motherboard belonging to a relatively nice but still not exactly new HP system…
Neither the ICH9 southbridge nor Win7 64-bit should inherently prevent you from properly accessing the 2.7TB (as to be reported by Windows). It’s likely drivers or BIOS limitations, if not some formatting quirk.
Check to see if HP has any BIOS updates. If so, you might find support there.
While we’re on the topic of the motherboard setup itself, check the BIOS setup to see if the motherboard detects the full capacity of the drive. Or you might see an option to switch the SATA controller between legacy/IDE mode, RAID mode, and AHCI mode. If not, then HP may have requested those settings be locked down, and there’s no sense worrying about them.
Ensure all the proper Intel drivers are installed and updated to the latest version. This may help you see the full size.
If all else fails, you may be stuck getting a SATA controller card with proper support for 2TB+ drives. (With the right card, performance should be just as good as with the Intel-sourced SATA ports).