This issue could be due to presence of static charges or internal hardware malfunction of the notebook. To isolate the exact cause of the issue, perform the following steps.
Step 1: Hard Reset
To perform a hard reset, please follow the steps listed below:
1. Unplug the AC adapter from the notebook PC and remove from any port replicator or
2. Remove the battery from the notebook battery compartment.
3. Press and hold down the power button for about 20 seconds.
4. Insert the battery and plug the AC adapter back into the notebook PC.
5. Press the power button to turn the notebook PC back on.
This will discharge the static charges from the notebook. Now check for the issue. If the issue persists, then remove and reseat the memory modules of the notebook.
Step 2: Remove and reseat memory modules
You can refer the service manual provided below for information to remove and reseat the memory modules.
Refer page no: 121, 122 & 123
PDF manuals require the Adobe Acrobat Reader for viewing and printing.
However, if the issue still persists, then it is clear that the issue is due to internal hardware malfunction of the notebook and requires a detailed onsite diagnosis by a service technician. At this point, I would recommend you to take the notebook to a nearest Computer Service Center to get it repaired/serviced. I hope the information provided would be helpful.