Some more information please.
1, Is this the first time McAfee is being used?
2. What security software is on there now or was there before and did you run the removal tool if available?
3. What operating system and service pack is in use?
4. How much installed memory (RAM) and free hard drive space (HDD) is there?
5. What errors if any have you been getting?
6. Where are you installing from - CD or online?
7. How do you connect to the internet?
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Customer Service (for account issues) is available Monday - Friday 0900 - 1700 via online chat or 0900 - 1800 via phone, again free.
To reach them click Useful Links at the top of this page.