Dell R630 iDRAC fails to initialize

Hi,

I have a Dell R630 which has been working fine for years, but recently I have been leaving it powered down (power cables still connected) and just starting it when I need it.  About a month ago iDRAC was unreachable.  I tried restarting the server, leaving cables unplugged and draining the flea power but still no iDRAC connection (could not ping or access the WebUI).  I ordered a portable VGA monitor and keyboard to see what was going on and finally last week I got around to connecting it all up to see what the problem is.  However after being left unplugged for a few weeks the error seemed to have cleared itself.  I then used it to test some SAS SSDs and then powered it down again.

Today I go to power on the server through iDRAC (which was previously working) and again no connection.  Connecting the monitor and keyboard I could see that there was no IP for iDRAC, that the start-up was taking a long time on Initializing iDRAC and then finally a message that iDRAC could not be initialized and then it rebooted with the fans on full.  No amount of resetting or draining flea power got it back to working.  I tried to access iDRAC settings from the BIOS but that didn't work either. 

What can the issue be?  I'm thinking it is some sort of hardware problem.  Can the iDRAC be replaced separate to the motherboard?

Thanks,
Al