OS X updates stuck on progress bar

Hi,

Trying to upgrade my Macbook Pro running 10.7.5 to either Yosemite or El Capitan and having a few issues. After restart I get stuck on a screen with the Apple logo and a progress bar, which has stalled at 50%, 90% or 100% depending on which system update I'm trying to do. CMD-L doesn't seem to work. Tried all the usual fixes I've seen online - waiting it out, rebooting, safe mode, PRAM reset, recovery mode and downloading a new OS, Disk Utility repairs but no success. Memory and storage is not an issue. I can Time Machine back to Lion pretty easily but it's a bit of a pain as I could do with some new programs which don't support my current outdated OS.

I have a late 2011 Macbook Pro - booting off a third party SSD, have also swapped the optical drive for a third party HDD which contains photos music etc - suspect this configuration is something to do with these problems but not really sure about how I'd go about sorting it.

Cheers