I was just wondering if you can take a photo useing the lcd screen on the pentax k100d

You are looking for a feature called "live view" which the K100D does not have.

That feature is called "Live View". The K100D camera does not support that feature.

More specification information can be found here

Regards,
Jacob

The best way to lighten the viewfinder is to purchase a new focusing screen. There are many alternatives available and usually cost around $100. There are specialty screens to allow better manual focusing and others that brighten the viewfinder. These effects are usually achieved through coatings on the screen. They are relatively simple to install, however if you are uncomfortable doing it yourself, a local camera shop should be able to do it in a matter of minutes.
This screen will allow better focusing of manual lenses and will also brighten the viewfinder, when you purchase the "Brightness enhancement treatment" option at the bottom of the page. http://www.katzeyeoptics.com/item--Pentax-K100D-K110D-K200D-K-r-K-x-Focusing-Screen--prod_K100D.html
The linked product also fits your camera, and the brand is highly regarded as being good quality. There are other options available though, simply search on B&H Photo Video or Adorama Camera. They have many different options.
B&H:http://www.bhphotovideo.com/c/search?Ntt=k100d+focusing+screen&N=0&InitialSearch=yes Adorama:http://www.adorama.com/SearchSite/Default.aspx?searchinfo=focusing+screen&category=4294962858
Thank you for choosing FixYa!

Pentax K100D does not have Live View function. So you can't preview the image before taking the image.

First make sure you are using fresh lithium batteries. These cameras indicate low batteries quite early on. Rechargeables even when freshly charged are marginal.

If the problem persists remove the batteries. Set the camera switch to the off position. Set the focus switch to manual. Wait at least a minute. Then replace the batteries and switch on again.

Operating with low batteries can confuse the firmware and it may be stuck in a low-battery loop. If this is the case this should reset the camera by allowing the electronics to power-down completely.

If this does not work you wiil have to contact pentax support.

Hi!
This is a feature and not a defect of the K100D. You can turn this off by going to the menu and going into the second tab (playback menu). Once there, go to preview display, where you will have 3 options - off, histogram and brighten areas. Set this to off (your camera is set to brighten areas, that is why the white parts of your photos appear to be blinking).
Hope this helps!

Read the K100D manual. Go to the Setup menu and allow for lenses with manual aperture settings.

Hi,
I assume that you are using Win.XP,
- did you check; System Properties>Hardware>Device Manager
Is there anything like yellow exclamation etc, especially on the USB section?
- Is it BIOS USB function enabled? Maybe disabled by accidentally.
- You said nothing working through USB, all ports are same?
If this ocurred all of a sudden, than I think you have a software problem.
I have a K100d, its been seven months now and ~6500 photo. My USB cables&fittings are fine, I always using USB port to transfer photos, no problem at all.
I hope your problem will be solved in a short time.
Sincerely
-halotheracer-

The interface IC ( between the main CPU and the CCD sensor ) seems faulty . Camera should go to the Pentax agents unfortunately.

You can select this preview option in the "custom settings", see page 103 of the manual (link below) http://www.pentaximaging.com/files/manual/K110D_web.pdf