Ordinary window screens (used at garage sales)( can be fitted with taffata, white cotton, white plastic) make great scrims and diffusers. cheap.

My very first "Pro" studio set-up...
I remember it well.
1 ceiling planter hook.
1 piece of white foamcore.
tin foil.
tape.
I affixed the hook at a 90 dergree angle to the edge of my largest north facing window, exactly the same distance as my curtian rod. I'd unhook one end of my curtian rod and swing it out and hang it from the hook to use my curtian as a backdrop.
White foam core with tinfoil taped to one side = 2 sided reflector.
Viv 285 for flash/hair/back/fill/colored gel effects.
Large north window = softbox.
White curtians.

I like Murphy's law.
I'm the only person I know that murphy's law actually works for me!
Murphy's law implies that if an airplane falls out of the sky and all but one passenger perish, the sole survivor, will be the one poor wretch whose life was so pathetic as to not be woth living. The one that would've been better off dead. That's usually me.
I never buy lottery tickekets, becuase I know I'll win, and then have a fatal accident on my way to cash it in.
I don't have to wonder about my luck, before doing anything dangerous. I know it's bad. Rather than ask if I'm feeling lucky, I just make a short list of all the people who've told me to "Drop dead" in the last week and ask myself "How lucky are THEY?".
For example I"m hanging off the strut of a plane a couple years back, and the skydiving instructor points at a video camera mounted on the plane, and asks me "Any last things you want to say to your wife?"
"EX-wife.." I reply "...YOU'RE NOT THAT LUUUUCCCCKKKKYYY!!!!!"

Here's a tip for those that have the right epson printers my r300 and I believe(not 100% certian as i've had no reason to test)my925 both have usb ports on the front and card readers. I've tried my r300, plugging an inexpensive cd burner into that port and cf/sd cards into the card reader.
The printer was able to print a contact sheet, and burn a cd off the memory cards.
My reason for posting this here? I ran it off an ac inverter in my van.

Ipod, Ipod, Ipod.
I've even resorted to giving my customers thier wedding albums/corporate shoots on Ipods.....
Requires a seperate adaptor though.
Did I mention I like Ipods?

By the way the screen should have one side that's glossy and smooth and one side that's matte right? plain rubbing alchol on the matte side may work with a makeup spounge to remove any residues.

Blurred and blotchy does not sound like scratched and damaged. Maybe try cleaning it again.
Here's my advice: use a micro fibre cloth, and Pledge furniture polish.
Sounds crazy and dangerous? yep. but what've you got to lose? It's already ruined right?
ps; I've used pledge successfully on my motorcyle, my helmet visors (it fills in tiny scratches), my Ray-Bans, and scratched cd-dvds. A little plastic or glass viewfinder screen should be doable. no promises though. let us know if it works?

JR is right, shutter most likely cause, faulty/dirty shutter release is another (less likely) cause (it is after all an electronic switch).

Define blank.
pure white-or pure black?
most likely a stiking shutter or a sticking diaphram.
Can't tell you which, with out knowing what u mean by blank.

Intersting read this thread, I've been using my 50 1.4 for portraits, with studio lights and a handheld meter, and no problems. I definately am tucking some of this info into a dark dusty crevice somwhere in the depths of my twisted mind filed under "good to know..."