What is the exact model number of your system and is the battery a genuine Dell OEM battery? Also check all the connections such as make sure the battery is fully plugged in to the MB.

Perform a hard reset.

1. Turn off the computer.
2. Disconnect the AC adapter or power cable from the computer, and remove the battery (for Dell laptops with removable battery).
   NOTE: For Dell laptops that have a nonremovable battery, see the Dell knowledge base article  How to reset Real Time Clock (RTC).
   For Dell laptops with removable batteries, see the  User Guide for your Dell laptop for step-by-step instructions to safely remove the battery.
   NOTE: On select Dell Latitude laptops, try to recover the laptop using the forced ePSA method from a POST or boot failure. To learn more, see the Dell knowledge base article  How to Use Forced ePSA to Recover from POST or Boot Failure.
3. Disconnect all devices such as USB drives, printers, webcams, and media cards (SD/xD).
4. Press and hold the power button for 15 to 20 seconds to drain residual power.
5. Connect the AC adapter or power cable and the battery (for Dell laptops).
6. If your Dell computer can turn on but is unable to boot into Windows, identify the symptoms and follow the appropriate troubleshooting guide.