I'd want to run the WD Diagnostics Data Lifeguard extended CD test which can be run from bootable Hiren’s BootCD 15.1
since the WD site is too incompetent to keep a good ISO download up for long before it goes away for a year unnoticed.
Then I'd run a Disk Check
from the booted Windows 7 DVD Command Line, on all partitions.
Both of these tests can also be run from free Partition Wizard
which also is on the Hiren's boot disk or flash stick. Partition Wizard Check File System Partition Wizard Use the Bootable CD
While you have PW booted, run Partition Wizard Rebuild MBR - Video Help
after checking the Active flag is intact on the correct partition as explained in the Troubleshooting steps, then run Startup Repair 3 times with Active flag on first SysReserved and then C.
I'd also use the other Hiren tool suggested in the steps too, to know you've done everything.