If your PC or laptop won't boot beyond the Bios screen, and you recently cleaned it inside, the culprit is likely to be a dislodged component. Our Helproom Editor explains how to solve the problem, and how to find out your Windows install product key.

QUESTION My Samsung R580 laptop was running hot, so I decided to dust the insides using compressed air. I earthed myself, then removed the RAM cover, hard drive, optical drive and part of the casing to get to the affected areas. I left the laptop a while for any condensation to evaporate, then switched it on. A buzzing noise is now audible from what I think is the hard drive, and startup won't proceed further than the Bios screen.

I used Windows 7 Image Backup to back up my data to an external hard drive. I also have my original Windows 7 installation disc, but no product key. What can I do? Anon

HELPROOM ANSWER It sounds as though you've taken the proper precautions, so we suspect your problem is likely to have been caused by a component becoming dislodged during the cleaning process rather than as a result of static damage or liquid from the spray duster entering the case. See also: Laptop crashes in Bios

Because the system is hanging at the Bios screen, we don't believe the hard drive is at fault. Try removing it from the laptop to help narrow down the problem. You will then know for certain whether the buzzing sound comes from this component.

A likely culprit is your memory. Carefully remove and re-seat the memory chips, then try to boot the laptop without the hard drive installed. The system won't boot, but you should at least be able to enter your Bios setup and perhaps receive an error message about the missing drive.

If this doesn't solve the problem and you have more than one stick of memory installed, try it with just one and then with the other, then repeat the process in the other memory slot. This will help you determine whether one of the sticks of memory or memory slots is faulty.

If everything seems to be working without the hard drive installed, then the hard drive could be at fault. If possible, check the hard drive by connecting it to another computer. You can do this by fitting the drive into an external drive enclosure, usually available for around £10, then connecting it to a second computer via USB. You can then check the drive for errors and perform any data recovery that may be necessary.

If the laptop appears to be working but the drive isn't functioning, you'll need to buy a new hard drive. You could use this opportunity to upgrade to a faster or higher-capacity model, or even an SSD.

If the drive is functioning, but the laptop still doesn't work, you may have to send it to a local PC shop for repair. Keep hold of your hard drive so you can reinstall it in the repaired laptop with your data intact.

If you do need to replace the hard drive, you'll be able to use your image backup to restore your data to the new drive. You will need your Windows 7 installation disc, but you won't need to know your product key – this will also have been backed up.

Boot from the Windows installation disc and select ‘Repair your computer', then choose ‘System Image Recovery'. This should allow you to restore the system image from your external hard drive.

It's a good idea to jot down your Windows product key. Use The Magical Jelly Bean Keyfinder to decrypt the product key stored in the Registry. (See also: Help! I've lost my Windows 7 product key.)

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