A very common problem with laser pointers and lasers in general that is easy to fix is dirty lens. I'll briefly explain the two safest and effective methods to clean laser pointer lens.
The equipment used in these instructions are
A Viper 95mW from Dragonlasers at http://www.dragonlasers.com
A lenspen from http://www.lenspen.com/
A squeeze bulb from ..... (no idea, its being lying around for a long time)
Step 1: Safety First
Safety is always an issue with high power lasers so the first thing you do when cleaning them is take the batteries out. A number of people have had unpleasant accidents cleaning lasers because they left the batteries in.
So unscrew the battery cap, remove the batteries and just to be sure, leave the battery cap off.
Step 2: Good and Bad Ways to Clean a Laser Pointer Lens
There are lot of different ways you can clean the lens of a laser pointer. They range from q tips and micro fiber to alcohol solutions and your finger (no kidding, some people think rubbing the lens with their finger will clean it).
Some methods work well, some work poorly and some will even damage the lens. The lens is very easy to damage and many people end up damaging their laser pointer's lens when they try to clean it.
There are only two methods that work well and will not damage the lens. They are compressed air and professional lens cleaning tools such as lenspens.
Step 3: Remove the Lens Cover
Gently unscrew the lens cover from the laser. If necessary apply pressure but do not force it.
Be careful once the lens cover is off keep your fingers away from the lens.
Step 4: Cleaning With Compressed Air
Hold the nozzle of the can or bulb close to the lens and give the lens several brief burst of air. Take care not to touch the lens. If you are using a can of compressed air, make sure you do not get any liquid on the lens.
Most of the time, compressed air will clean the lens.
If the lens is still dirty, use the lens cleaning tool.
Step 5: Cleaning With a Lenspen
Only use a professional lens cleaning tool such as a lenspen if compressed air does not work.
Very easy to do, just gently polish/clean the lens with the tip of the lenspen. Should not take more than 2-3 seconds.
Step 6: Put the Laser Back Together and Test the Beam
Assemble the laser and test the beam.
it the lens was just dirty and not damaged, the beam and beam point should now be very clean and have good quality. If the laser still has a problem, the lens is probably damaged.
The beam point should look like the one in this picture. The halo is small and has no scatter or other defects.