HD MBR problem

i dunno where this thread should be located really but all i know is that

i was resizing my partitions when a power out happened
only the biggest one was hit ,
it was 282 gb now its 278 and 4 gb unallocated after the patrition at the end of the disk i opened up windows to see what happened ,i also would like to add that that partition is highly fragmented so after 4 gigs were unallocated at the end of the partition i ended up with alot of corrupt files so all i managed to was to modify the mbr to make the 4 unallocated gigs be at the start of the partition between the others,and other files got corrupted but others were fixed

how do i modify the mbr to make the partition 282 again without formating of course