Troubled Zero

Having lost my business in june 2022 through no fault of my own I have been somewhat forced into semi retirement, this is not something I wanted to do and it has had a seriously negative impact on my health both physical and even more mental. So I purchased a second hand cnc machine just for something to play about with, never even seen one before so it was something completely new.
I learnt how to use the mach 3 software and managed to cut and v carve some nice pieces. However now the machine isn't working as it should, after setting the v bit to zero and starting the machine, whilst its doing its thing the cutter somehow dosn't follow the g code properly and ends up with the engraving being off centre to the right, and when it moves back to the zero the cutter goes past the zero point by anything upto 2 cm, it only does it in one axis and its always to the right.
Does anyone have any suggestions to resolve the issue.
Many thanks Bolly Wood