Make sure that your phone IMEI is same as the one shown on the box.
Also not a blank IMEI.

that's weirdo on SIM tray man..

Though I have not encounter this issue but yes, there is a possibility.
Also search around, seems like this is one of the common case for N5. Are you able to claim warranty?
When you do manual search, and click the network, what's the error message it show? Just "can't register to network"?

Hmmm..
The exact message is "can't connect to this network right now. Please try again later"

Also, i did some search on blocked imei. My imei turns out blocked in canada. That does not applly here right?

Hmmm..
The exact message is "can't connect to this network right now. Please try again later"

Also, i did some search on blocked imei. My imei turns out blocked in canada. That does not applly here right?

Canada set? btw, where you got the set from?   

  If an IMEI is blacklisted/blocked, there's a strong possibility that the device is stolen,lost,etc.
Where did you get your phone from?

Nope. Bought from OZ playstore. Then a friend helped bring it back.

If i send it back, should i relock, unroot etc before sending for warranty? If my rooting caused this, they still honour the warranty right?

No mood for work liao liek dis.

Let me find back the link to check blocked IMEI then you check yours. Mine is D821 OZ play store set

I believe there's a temperflag in the bl that checks if you mess with the bl before. So I recommend to just flash back to stock image, unroot, relock bl, reset the temperflag before sending back for warranty. Think in xda posted before how to reset temperflag.

I believe there's a temperflag in the bl that checks if you mess with the bl before. So I recommend to just flash back to stock image, unroot, relock bl, reset the temperflag before sending back for warranty. Think in xda posted before how to reset temperflag.

here's the link for temper flag, i unlock, root, unroot, lock for like 3 times d...still waiting replacement phone arrive.
http://forum.xda-developers.com/showthread.php?t=2513701

between, this is my phone battery rate, is it ok?

Thank you for the link 

What's your SOT? You set location to High or device only? GPS is pretty much on whole time.
From the "awake", your phone barely goes to deep sleep, there's wakelock. (I assume it's the weather widget which consume 80%!omg )
You barely on wifi as well.

Done that. to confirm this, is by bootscreen without unlocked icon & fasboot status : locked?

here's the link for temper flag, i unlock, root, unroot, lock for like 3 times d...still waiting replacement phone arrive.
http://forum.xda-developers.com/showthread.php?t=2513701

between, this is my phone battery rate, is it ok?

dafuq that weather widget 

dafuq that weather widget 

pro widget bro 

LUL! I know right. 80% omg
I would suggest you update it manually. Or at a longer period (eg: every 3 hours). Will eat less of your battery.
Can post SS for that weather widget?

here u go, if im not mistaken i set update every 1hour

received my SGP casings today.

That was fast, less than a week and I received them already!

bought the clear crystal shell, bright red neo hybrid, and white slim armor.

sporting the white slim armor for now

The bright red neo hybrid is exactly the same red as my red nexus 5. Sweet!