Cannot boot to boot camp Windows after shrinking the Mac os partition

I have a Macbook pro (Retina, 15-inch, Mid 2014, "El Capitan"), also contained a BootCamp partition - installed Windows 7 after the partition was created, and then upgraded to Win 10 later.

After I used Disk Utility (GUI) to shrink the mac partition, I can't boot into Windows anymore (Mac OS still work, posting the post using it now).

However, in Mac's Finder I can still read the files in the BootCamp partition, seems that the partition is still intact.

Tried building a "USB recovery disk" created from another Windows 10, boot from it, and used its "auto fix" feature, but it didn't work. I can still fire up the command prompt though, so I should be able to do things like bootrec, fdisk etc.

Is my Boot Camp sort of a "Hybrid MBR" thing? I tried to get more info about how my machine's partitioned, but I dare not do anything drastic as I fear that I might broke something again.

1. What should I do to make Windows work again?
2. Is there a way to let me back up the partition layout (instead of the partitions themselves) so that if I screwed up fixing the partitions, I can safely return to the point before things were screwed up? I'm sure that the partition info should not take a lot of spaces.

Not sure if it helps, but here is what diskutil and fdisk (in Mac OS terminal) shows (the disk0s4 partition is got as a result of shrinking the Mac partition):

xxxx$ diskutil list

/dev/disk0 (internal, physical):

   #:                       TYPE NAME                    SIZE       IDENTIFIER

   0:      GUID_partition_scheme                        *500.3 GB   disk0

   1:                        EFI EFI                     209.7 MB   disk0s1

   2:                  Apple_HFS Macintosh HD            120.1 GB   disk0s2

   3:                 Apple_Boot Recovery HD             650.0 MB   disk0s3

   4:                  Apple_HFS Untitled                29.2 GB    disk0s4

   5:       Microsoft Basic Data BOOTCAMP                350.0 GB   disk0s5

xxxx$ fdisk /dev/disk0

Disk: /dev/disk0	geometry: 60821/255/63 [977105060 sectors]

Signature: 0xAA55

         Starting       Ending

 #: id  cyl  hd sec -  cyl  hd sec [     start -       size]

------------------------------------------------------------------------

 1: EE 1023 254  63 - 1023 254  63 [         1 -  977105059] <Unknown ID>

 2: 00    0   0   0 -    0   0   0 [         0 -          0] unused      

 3: 00    0   0   0 -    0   0   0 [         0 -          0] unused      

 4: 00    0   0   0 -    0   0   0 [         0 -          0] unused