HELP - My new Nokia Lumia 620 won't boot up, even ...

Question

I'm worried my Nokia Lumia 620 is a lemon, and the Care Centre will just keep taking it in for repair.  The reliability so far has been disappointing, especially as I was giving Nokia a try after a 10 year break, and also trying out Windows Mobile / Phone after a 6 year break.  I want to recommend it - I'm continually being asked by friends and colleagues what I think of my new phone.   Nokia will be smart to just replace it.      
The details: my Nokia Lumia 620 won't boot up today (again).  It hung on boot  this morning with the Nokia Logo.  That was over 2 hours ago.  It had this problem during February, and I returned it twice for repair to the local Nokia Care Centre.  I guess I'll take it in again later today, but it just feels like a lemon handset so far.
Timeline:
Handset purchased in local Nokia Store on Jan 29 2013 ( 7 weeks ago)
Handset gave "Exclamation-Mark-Screen-of-Death" on Feb 19 2013 (3 weeks old handset)
Local Nokia Store sent me to local Nokia Care Centre, handed in overnight "for repair"
Phone returned on Feb-20-2013 after software refresh. 
Worked fine for 1 week.   Problem returned Feb 26 2013. (4 week old handset)
Nokia Care Centre "replaced motherboard" on Feb 27 2013. 
Has worked fine for 3 weeks.   Now Lumia 620 won't boot this morning - no Exclamation Mark, instead it's the Nokia Logo on boot.  
The handset is 7 weeks old.
Hard reset (side-button-combination) hasn't worked either.  
Any advice on getting this working, repaired or replaced?

Answer 1

   Update on the repair - it didn't work.   I returned the phone to the Yau Ma Tei Nokia Care Centre on March 20th, and was given what was termed a 'replacement' phone.   I was pretty happy.  All was well.  But two days later when I tried to make a phone call using my headphones, I noticed that only the left audio channel was working through the earphones.   I tried a second pair of earphones and the same problem.    The audio was only working through the left channel.  On a new phone.  How strange.  
So was it really new?   My suspicion is that the repair centre has used old returned parts (parts they perhaps term as refurbished) - so in fact my replacement phone is my old phone assembled with old and refurbished parts.   Was it in fact a refurbished phone assembled from refurbished parts?   Frustrating when they tell me it's a replacement phone.  
That was back in late March.  I posted a couple of tweets and Nokia responded.  They even phoned me to try and help.  However no offer of a new phone.  All they suggested was that I revisit the Nokia Service Centre.   For a 4th time.   
That was about 6 weeks ago, and I simply haven't made the time to go to the Service Centre again.   It's hard to find the time when my last 3 visits have been so unsuccessful.
 Sometimes you just get a lemon.   It happened to me once before with a different manufacturer when I was on a contract and had to live with a phone for 2 years that kept cutting out during calls.   Same problem - the manufacturer attempted to repair it, but it just never worked properly.   That was 10 years ago.  Now it's happening with my new Nokia.  Luckily I'm not on contract this time.  I've read good reviews for the Lumia 620, and overall it's a pretty decent handset in every other way.  
But the issues this particular handset has been plagued with has overshadowed any positive feelings I have been having.   I'll probably be cutting my losses and changing handsets in the summer.