Using Windows XP....
Does anyone know far back you can restore your PC to an earlier time....???
Hard to say. It depends on your specific computer and usage.
The maximum amount of restore points possible depends on how much disk space you have given to System Restore: Right click on My Computer, Properties, System Restore. Another limiting factor is how much system changes you make (a new restore point is created at every important step) and the fact that you get a new restore point every 24 hours too.
SR wil also delete some of its data when the amount of free disk space is very small.
The dates with available restore points will be shown in bold.