X51 R1 Powerboard upgrade gone wrong

My R1 is an old desktop, probably 5 years old already.

Recently its (second) GPU, GTX 660 died. I would like to take this chance to upgrade it, so I did some extensive research through the forums. I found out that the R1 power board is a bottleneck to better GPUs.

I know that the R2 power board isn't an official spare part to use for R1, but I have read tonnes of forums and with countless stories that it works. Hence, I've end up getting a R2 power board (D85RT) from Dell Sales Team.

Managed to place it in with all the cables attached. But when I tried to on, no power seems to be flowing in the system. Checked the cables, everything is attached, but still no power. But when I fixed back my original R1 power board, everything seems normal (no cable broken etc.).

I'm always impressed with Dell's service response, but not so sure about the spare parts though.

But before concluding that the R2 power board is faulty, what could be the possible causes preventing it from turning on?

i7-2600
(2x4) 8 GB RAM DDR5
No GPU currently, GTX 1060 FE otw.
330W PSU
BIOS Ver. A14
Windows 7