2. Disable all security software: anti-virus, firewall etc. Remember to enable afterwords.
3. Make sure your computer has the most recent drivers.
4. Disconnect all external devices except keyboard and mouse before installing.
5. Unplug your computer from the internet, if you have wireless disable it. Do not select to get updates during the install.
6. If you have multiple hard drives remove all except the one you're installing Windows 7 on, then replace after Windows 7 is installed.
7. If you downloaded Windows 7 and burned it to a DVD try burning it again at the slowest speed possible. It's also possible the download may have errors, you could try downloading it again.
8. Disable Startup Programs:
A) Click Start, type MSCONFIG in the Start Search box, and then press Enter.
OK User Account Control permission and enter password if any
If using XP: Click Start, click Run, then type: MSCONFIG and click OK.
B) On the General tab, click Selective Startup.
C) Right below Selective Startup, uncheck the "Load Startup Items" check box.
D) Click the Services tab, click the "Hide All Microsoft Services" box, then click Disable All.
E) Click OK, then restart the computer.
F) Attempt the upgrade again.
(NOTE: if the upgrade doesn't work and you continue to use XP/Vista turn your security software back on, then also return to MSCONFIG and on the General tab, click "Normal Startup" then click OK to exit.)