computer lock out

My laptop inspirion 5000e recently had some repairs done to it by dell when i put the hard drive back into it the computer continues to crash going to the physical memory dump screen. Now most of the time it will not boot up past the screen that says press f1 to continue or f2 to go to setup. Sometimes a screen comes up saying windows could not start because the following file is missing or corrupt: System32/DRIVERS/pci.sys. How do I repair this problem?
Thank you