if he change the motherboard with new one and connect it with my old hard drive, Is it possible to access the old windows ?
Short answer: Yes
I have swapped out a motherboard and been able to access the Windows install that was on the hard disk in the system prior to the motherboards.
In hundreds of cases, I have advised technicians I was supervising to swap out motherboards as well.
In all cases where the existing hard drive was not damaged prior to my technician arriving on the customer premises, the Windows install was accessible once the failed motherboard was replaced.
The only possible hang-ups I can see would be if the motherboard was not very similar to the old one and your system's Windows install was under an OEM license. In cases like this, you or your technician may need to contact Microsoft for assistance with activation. In certain
circumstances, you may need to purchase a new license.
Unless you have been advised that there is to be a licensing issue, it is reasonable to assume that there will be no such issue.