HP Color Laserjet 2500 colors problem

Question

Helloo! 
I have a problem with my HP Color Laserjet 2500. I use Windows 7 proffesional 32-bit computer. Installed driver from hp support, because the CD that came with the printer, is only for XP/ 2000 /ME etc. I tried both, the PC5 and PC6 driver, always the same problem.
I can print, but i have one problem, and few questions.
Problem: Sometimes it prints only yellow color, sometimes only magneta. Sometimes it combines blue and magneta, and leaves black and yellow out. And sometimes, it prints all the colors. I could say, that almoust 50% of the times, it prints normally. When it does not, it prints like i desicribed above, in all different possibilities, sometimes doesn't print yellow, magneta, blue or black. Sometimes it doesn't print two colors, rearly prints only 1 color, and even more rearly (happened about 2-3 times) it doesn't print anything. It has been a problem for years since i attached it to the Win7 computer, but at first it worked great. Then sometimes it messed up 1 document in a while, then 2, then 3 in a week. But now it's bit more than 50% of the documents that it messes up.
Quesion 1: It appears, that when i choose Printing Preferences in the computer, it displays some different language, i think it's arabic!? Written from right to left. How can i change that?
Qouestion 2: I can't find my products serial number. When i print out the configuration page, it says Printer Serial Number: CNHDD06356, but when i post it in the HP Chat Support, it gives me error. What am i supposed to do? 
If you solve my problem, i will buy you a beer when we meet!
PS. What i've tried:
Cold reset.
Different drivers.
New USB wire from printer to computer.
All cartridges have over 40% ink in them. Black 44, cyan 97, magneta 76 and yellow 97%.
Imaging drum is practically new, shows 93%.
Cleaned the printer inside.
Added a bit WD40 to moving parts.
Now i'm hoping you can help me..
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Answer 1

Hello again!
I SOLVED IT !
Who ever, when ever will have the same issue, here's how i fixed it (sorry for my not so correct english):
I googeled around a bit more, and found a topic in some forum:
http://www.fixyourownprinter.com/forums/printer/68382
http://www.fixyourownprinter.com/forums/printer/63372#1
And then i saw a video in here:
https://www.youtube.com/watch?v=9BoxmagIjhg
What i did:
Took the printer apart. All the plastic covers. I think i only had to take 2 screws out, to cet the covers. I only didn't take down the cover where you can put paper in, i didn't need to.
The cover where you put colors inside was tricki. The lid communicates with other pinions, so you'll have to remove it. To remove it, there is this little black pinion inside the printer. In the center of the pinion, there is a buttonish thing, you'll have to push it to the side ways, from center to edge to remove the pinion and then you'll be able to remove the top plastic cover.
Then i did as it's shown in the video:
https://www.youtube.com/watch?v=9BoxmagIjhg
You'll have to clean this "solenoid" thing. I used a little knife to scratch off the clue from both pieces. There was supposed to be a felt, but mine didn't have it anymore, and THAT was wat was caousing it. 
IMPORTANT: My felt from the solenoid was cone, so i replaced it with masking tape. I  cut a little strips out off of a masking tape and clued/wrapped it around the solenoid. It is recommended though, that you clue a little felt back in there, but i didn't have it, so i used masking tape.
Then i put all the pieces back together and it worked ! 
You cant believe my happiness, when it started to print every paper correctly. I had this problem for a while,  and unbelievably this worked. 
If you have the same problem, i hope this trick will solve yours too.