Second first print is horrible  

I assume you got new fan that's identical to original (5V, 8000 rpm max) and that it's connected properly. In this case I think, it's just a coincidence that you have this new problem right now.
I would just check "usual suspects".. make sure first, that bed is clean and filament dry.
Next thing that could happen (at least my theory), depends on at what point your fan died. If fan stops working at the middle of the print, then the temperature inside heatbreak (at the coldend side) will start to raise quite fast and so it's possible, that the filament melts inside PTFE tube. Maybe you should take hotend apart and check if everything is ok inside.

Just sharing my thoughts

The three common reasons for prints suddenly failing after a printer has been unused for a while:

A dirty print bed.  Give it a really thorough clean and avoid touching the print area.

Damp filament.  Look up threads here about drying filament especially if it has been left open.

General neglect, dust and cobwebs...  Basic cleaning, lubrication and general maintenance have all ben missed.  See: https://help.prusa3d.com/en/article/regular-maintenance-mini_133222

Cheerio,

so far so good

Thanks for your advice. Because it looked more like bad adhesion I started by cleaning the print bed thoroughly. I couldn't find IPA 90% so I used medicinal 70% alcohol. Did a couple of easy prints and so far so good 🙂

Dish soap

If you are still having adhesion problems, try washing your sheet with a small amount of dish washing detergent. IPA doesn't cut the grease from fingerprints as well as soap. Also make sure your alcohol is pure IPA. Some products have additives that will defeat the purpose. 

Thanks

Thanks. Actually the 70% alcohol I used works flawlessly. However only when I wipe with paper, and not when I wipe with microfiber towel 🙄

Microfiber

Microfiber towels can have treatments on them and can hinder cleaning.  

Posted by: @gald33

Thanks. Actually the 70% alcohol I used works flawlessly. However only when I wipe with paper, and not when I wipe with microfiber towel 🙄