corrupt files and memory write/read failure error

Several weeks ago, my computer encountered a problem and windows shutdown to avoid damaging the computer. When I rebooted my Inspiron 8200 notebook, I received the following error. Windows could not start because the following file is missing or corrupt: \windows\system32\drivers\isapnp.sys. I also received a memory write/read failure error. I replaced the corrupt file but continued to receive error message. I attempted to reinstall windows, but received another error message during the reinstall, causing my hard drive to crash. A diagnostic check reveled four uncorrectable errors on my hard drive. I called Dell tech support and was advised to replace the memory and hard drive. I installed a new hard drive and memory and installed windows xp. Unfortunately I encountered the same problem as before with the old drive and memory. What is causing the files to become corrupt and the memory errors?