Adkel,
What are the particulars of your system? Did you build it or buy it off-the-shelf? Was the repair tech independent or factory authorized? How did he reinstall your operating system and/or applications, from installation disks or recovery disks? Yours or his?
The reason I ask is that some OEM systems' recovery disks can only be used with the system they were shipped with, usually just the same model but sometimes the same system. Also, some manufacturers have custom installations to deal with proprietary hardware, i.e., requiring custom drivers, and you must use the disks supplied with the computer. Did he fail to install any updated drivers that you had installed yourself, chip set, video card, etc.? Conversely, did he install updated drivers that you hadn't, drivers that may be incompatible?
Take it back to him, and If he screwed up, make him to the job right. Insist that he credit you with the amount you've already paid. If you used a credit card, make it clear that you will contact your credit card company and request a charge-back if he doesn't provide the service you paid for, to restore your computer to proper working order.
Regards,
Hornus