398349 Computer lock-up utility

I run a company that finances computers. If the customer does not make his monthly payment then i want his computer to lock until he does so. I want this to be designed into the CMOS Bios (if possible) as opposed to the operating system since if windows is reinstalled then the utility installed would also be removed. My vision is: If the customer does not pay his monthly bill then his computer needs to be locked up. Once he makes the payment, i can provide him with a code that will allow him access. Each code could be used only once and the computer must not lock up until the customer misses another payment. I should have a list of 36 codes installed on every computer where each code is good for 1 use, meaning good for that month. so if the customer finances a computer for 3 years then i should have a maximum 36 codes (1 for each month) on the basis that he misses every payment. Obviously a good customer shouldn't be missing any payments! hope this is quite clear... happy bidding!