I suppose it could be a problem with the camera's power switch, does it function correctly in other respects?

I'm not really bothered, I and I'm sure many others will be using their film cameras for quite a few years yet.

I did like some of the comments that were posted tho'

Unfortunately, no amount of blowing can shift particles from behind the screen, so it has to be removed. The penta-prism (or in my case mirror) housing is sealed by the screen itself - but obviously not completely.
I was quite pleased with my efforts, no visible particles and the hair had gone but lo and behold, the next time I used the camera, a couple of black specks were once again visible.
It's not too bad and for fear of scratching the screen again, I'll leave it for now but I think this might be either a small design flaw or perhaps there's a larger gap between the screen and the foam dampers than there should be.
The movement of the mirror must have dislodged the new particles so that they've come to rest on the screen.
This is something that I've never experienced before with SLRs, so that's why I'm supposing that it might be a design flaw, perhaps only affecting the DL and maybe only a few examples of that model.

This is where you have to be very, very careful - I've managed to put a tiny scratch on mine (but at least it's now nice and clean).

If you tilt the camera back, you'll notice a metal frame around the edge of the screen. At the top, in the center is a small tab, gently press this upward and the frame is released but you'll probably have to carefully prise the frame forward slightly before it lowers enough for you to access the screen.
Take care not to damage the foam mirror dampers.
It's quite a fiddly operation and it was while trying to lower the frame that I scratched the screen

The screen has a small tab to the bottom right-hand corner so that it can be handled with a special pair of tweezers - I strongly advise that you use a pair

After gently cleaning the screen, replace it into the frame and carefully push it back up into place, where it should click securely.

There is no doubt a special tool for releasing the screen frame but a ball-point pen tip is fine enough to press the tab but the tricky bit is getting the frame to drop while holding the tab in the release position because the tab is part of the frame - so it's pretty much a two-handed operation!
If you can imagine, you have to try to press the tab inward/upward while at the same time prising the frame forward, it may take a couple of attempts so don't get frustrated and careless - which is how I managed to scratch mine

Perhaps someone else has a better technique but apart from being fiddly, it wasn't too difficult but please don't try it unless you really, REALLY need to.

I must admit that I've only used it on lenses so far but I believe it's perfectly safe - particularly with the power off and batteries removed.
You don't get a 'shock' from the device, it's just an ioniser and it's safe to use on hifi turntables. The technique is to squirt the ions onto the revolving vinyl record to eliminate the static and it really does work.
If I remember correctly, the ions are positively charged whereas the electrons that cause static are negative.

Thanks for your concern Matt, but I've got to get rid of those pesky particles.

I've got a bit of a problem with dust specks and tiny hairs that appear to be behind the focusing screen of my DL.
They simply aren't visible with the naked eye but irritate the hell out of me when using the viewfinder. It's quite easy to remove the screen but all attempts to remove the offending objects, using a blower-brush, have only made things worse.

I think the problem with brushes is that the bristles store particles from one job and deposit them on the next

What I've used before to good effect, and will try tomorrow, is one of those anti-static squirter things, sold in hi-fi stores. They look like gas lighters, where you squeeze a trigger and get a spark but in this case, you get a squirt of positive ions (I think that's right!). Anyhow what happens is that the ions reverse the polarity of the static that causes the dust to stick and the particles 'leap' off the surface that they were formerly so attached to. I then use one of those mini battery operated vacuum cleaners and hey presto - job done, hopefully!

I presume the same technique would work for the sensors too.

I'll let you know how I get on

That's it, I'm convinced...............this Pentax gear is pretty good (who cares what the reviews say!)

Lovely shots Joshua and that's exactly the feeling I get too and you learn so much from the ones that don't quite work, don't you?

I send my films away for development and it may have taken weeks to finish each one (I have several cameras and not nearly as many photo opportunities as I'd like), the excitement and expectation I have when opening the envelopes hasn't begun to diminish yet - and I'm sure it never will.

Digital's great in so many ways but I still love film.

Have you been able to remove the lens from the mount ie. leaving the mount on the camera body?

I have the 500mm mirror lens too but have had no problems except for the mount being a little tricky to align correctly - presumably because of the fixed aperture.

As you're having trouble removing the lens, I'm wondering if it might be easier to seperate the lens from the mount first and then try to remove the mount as if the lens were still attached.