Tough crowd
Well for anyone starting out like me who finds themselves in this situation here is the fix that worked for me.
First check the integrity of your HDD, there are countless tools to do this, no doubt in built VMware tools but I booted from a CD and carried out the task that way. No issue with my HDD.
So I reinstalled ESXi and selected the option to reinstall ESXi whilst retaining the data store (so it was there after all and for whatever reason had become invisible to my ESXi host). Once this was carried out and ESXi configured with the same details as the original version I was able to reconnect to my ESXi host and also I could see my data store. Browsed my data store and thankfully all my VM’s were still there. The VM’s were not listed in my inventory so open each VM folder, you'll see a .vmx file, right click it, add to inventory.
I’m back up and running now.
Installed Veeam and have backed up and set a schedule for continuous backups.
Thanks to the hundreds of people who viewed this post and offered not a single word of help. I hope this helps someone STARTING OUT like me.