No X on Dell Inspiron...
 

Where do we start diagnostics here?

It's a recent download of 10.04LTS.

Laptop is a new Dell i5 Intel, no dedicated graphics memory.

Seems to almost finish loading in a live environment, then lose display (purple background)

Is it a newer i5? It may be possible that 10.04 is to old for the graphics chip in the newer i5 CPUs, so it would help if you can give us the exact CPU model.

Could be too old - I don't know. I DID presume that a NEW 10.04 iso would be capable...

I went right to 'Install' (instead of 'Try'), and it has now booted successfully.

Intel HD 4000 is video adapter
Core i5-3210M is CPU ID...

Ubuntu 10.04 comes with kernel 2.6.32 and xorg-server 1.7.6, which are simply to old to have appropriate drivers for your GPU.
Try it with 12.04.

If, for some reason, you insist on 10.04, I believe that backported drivers are available for the Intel HD chipsets on the Launchpad PPAs...