You have less than 10% of available space on that hard drive. It's time to retire it. ASAP.
Back it up and get a new drive, saving two backups of your image files in the process.
Metadata should be preserved and new thumbnails will be generated when you purge the cache, but it can be a time consuming process.
Is that drive also your boot drive? If it is, then you're in a heap of trouble already. A measly 45 GB is not much to be shared by Photoshop's scratch file and the swap files of the OS, let alone to accommodate the cache.
Ok thanks I am currently copying one folder 340Gb to my external HDD and then I will delete this folder from my pc. This will free up the lack of space on my hdd.
Yes this hdd is my boot drive and it is a raid 1 configuration (2 x 500Gb drives) set up.
If I free up this hdd space do you believe the purging process will still be a wise step to do? As I currently 100% rely on seeing the thumb nails & high quality resolution to do editing?
Yes I am a novice learning adobe photoshop and any constructive guidance is much appreciated, please.
The thumbnails will be re-generated, that's not an issue. It's only a matter of patience. Just let it rebuild overnight—or longer if necessary.
On the other hand, see what happens once you free up space. The application may be able to function normally after that without nagging you to purge the cache.
In any event, I prefer to use the Purge Cache For This Folder command in the Tools menu of Bridge, rather than using the global Purge Cache command in Preferences.
Having a dedicated, physically separate hard drive just for Photoshop scratch will improve Photoshop performance considerably.
I personally keep a dedicated, physically separate 160 GB to 300 GB internal hard drive as Photoshop scratch disk. Figure on 50 to 100 times or more the size of your largest open file multiplied by however many files you keep open at the same time.
Bridge is the Achilles heel of the Photoshop application and, alas, the stepchild among Adobe's suite of applications. It doesn't get nearly the attention and resources it needs.
You may want to take a look at the dedicated Adobe Bridge forum: