If a printer is an output device, how then will you explain OUTPUT DEVICES to a beginner in computer technology?

My friend has got HP laptop and it cannot start up showing a screen with some ''F'' keys that suggest some tests. When I clicked F4 it showed ''hard disk not exist''. Also no mouse pointer was showing. How can I solve this problem?

Suddenly all my folders and files disappeared and computer stopped working .

When i restarted it and check the ''show hidden files'' option,all files and folders appears again.

But now the problem is occurring frequently.

How to solve the problem?

I am suffering from a problem with my USB port.My computer founds any devices containing USB port but not showing it in the "my computer''.how to fix the problem?

How effective is the universal battery when used against the original battery of my laptop?

What is wrong with my laptop battery since it keeps on charging for many hours?

What shall I do whenever my system prompts me that my system has low virtual memory?

My laptop always shuts down itself after 2-3 hours of use. I don't know if the problem is my battery or power adaptor. It doesn't want to start after shutting down. Then, it can be used again after 1 day.

Need help with this.

What is the compatible Antenna for this WiMax modem I have this modem from Samsung but it's antenna is 2DB i want a 12DB Antenna for this modem and for Wimax model Samsung CPE SMT-S3500?

I have a Blackberry Curve. I am surprised that it doesn't have application of radio application. Can anyone suggest me good application and from where should I download?