Very commonly Compaq laptops will have an issue when the battery has been completly drained, where it will display the Compaq logo and goes no further, this is very common and nothing to worry about as it is very easy to resolve.

One easy method is too clear the cmos:

Step 1  Remove Power cord.

Step 2  Remove Laptop battery.

Step 3  Remove CMOS battery, on the units I carry it is located under the keyboard which lifts up easily by depressing 2 small tabs near the space bar.

Step 4  Leave all 3 items removed for 5-10 minutes or longer. This clears the cmos.

Step 5  Hook everything back up and unit should function perfectly. We suggest always keeping at least 10% battery power in your unit if it is not plugged in if not more.

Another method:

Hold down the Function key, turn the machine on and tap the F11 key a few times in the first few seconds of the boot process as the splash screen displays. A '162' error message comes up. Hit F1 to accept the error message, the BIOS is reset, and the machine will continue to boot.