Tried to mirror system disk using windows 7 built-in RAID0, failed. Backup images were useless because HDD was converted to dynamic disk. Tried countless solutions. Finally, the following comamnd

bootsect /nt60 sys /mbr

worked.

Many thanks to ValiancyHe and his/her post(http://www.cnblogs.com/ValiancyHe/p/3398899.html)