I have a Dell Latitude C640.I keep getting a "Diagnostic Boot Selected" message on start up.
I have to keep hitting the escape key to by pass this extremely long and annoying POST.
After hitting the esc key repeatedly, it boots just fine.
I went into the BIOS to make any changes I thought might stop this but nothing seems to work.
I formatted the HDD,swapped out the HDD, replaced the CMOS battery, even went so far as to swap out the mainboard and I still get that same message on start up.
Has anyone else experienced this?
If so, did you find a fix for it?
I have a sneaking suspicion that the message might be originating in th Eeprom.
Any ideas or help will be greatly appreciated.

Hello,

This is Richard from the Dell's Online Community Outreach group. What you are experiencing is very unusual. You have reported that the system keeps booting with the "Diagnostic Boot Selected" message. But, the hard drive and the motherboard have been replaced which is basically equals almost a new computer.

With this type of situation I would have suggested to reset the bios defaults. The do this press ALT+F while in the bios. However, you have replaced the motherboard so I can't say for sure that this will correct the issue.

Try it anyway and see if it works. Best of luck!

Regards,

Richard B
Dell Online Community Outreach

I know you said you replaced it, but it could be worth checking that the new CMOS battery is ok, and making a good connection. If the cable connecting it is loose or internally broken, then it could be causing some settings to be lost each time the machine is power cycled, and lead to the machine booting in diagnostic mode.

What does the BIOS say your service tag is? There are some instances where a motherboard will remain in a manufacturing or diag mode until the service tag is set by a tech. However, the only time I've ever had such an issue was with an Optiplex desktop, never a Laptop.

Steverino's suggestion is what I'd try first, replace the CMOS battery. They're a bit tricky to find. If nobody on eBay has one you can always try Batteries+ if you have a store in your area.