HP dx2420 - Microtower PC Service & Reference Manual page 90

Computer will not start.
Cause
Wrong memory modules were used in the upgrade or memory
modules were installed in the wrong location.
84 Appendix C Troubleshooting
Solution
1. Review the documentation that came with the system to
determine if you are using the correct memory modules
and to verify the proper installation.
2. Listen for beeps from the computer. See
POST Audible Codes on page 85
causes.
3. If you still cannot resolve the issue, contact Customer
Support.
Interpreting
to determine possible