Analogue-sequencer

Hi,

I'm hoping somebody might be able to help me (I'm new).

This week I purchased an older P3 (one of the non-factory versions). 
This P3 does not have the latest OS installed.  I for some reason 
thought I would need to install the bootloader update found in 
the 'files' section which I have done. I am now receiving a 
message 'Not for this CPU' when I turn my P3 on. Clearly I have made 
a terrible error.

There seem to be 'other' versions of the bootloader in the 'files' 
section but rather than continue on my path of destruction I thought 
it might be better to ask for guidance.

Have I made an ireversible mistake ?  If not, which sequence of 
updates do I need to apply in order to bring my P3 up to the latest 
OS ?

Any help massively appreciated.

Cheers

Simon