Use free Partition Wizard bootable CD to make these kind of changes, Using PW CD you can also sometimes repair damaged MBR by clicking on the HD and from Disk tab select Rebuild MBR, too, which is why I mention this now to give you every option.
However you already have C set as System Active so it should boot if that HD is set first to boot, unless infected or in need of Repair.
in Safe Mode or Microsoft Standalone System Sweeper
from CD or flash stick.
You may need to run Startup Repair more than once so it can automate System Restore,and SFC, Then I would also try running them separately from the disk's tools list. SFC -SCANNOW Run in Command Prompt at Boot
I have to go now so someone else will help you get these done and answer your questions and if necessary we can continue tomorrow when we have your results reported back fully.