I need to know how to reset a T642, T644, X642 and a X644 Lexmark printer. But I can't seem to find this information properly. Could you help me out and tell me in detail how to do this for each of these?

On the left side, near the pichup roller, of the tray there should be a "flag" hanging down in the elips hole. See if it is hanging down or stuck in the "up"position.
If so pul it down and the machine should work fine again.

Lexmark T640 T642 T644 Fuser Maintenance Kit Replacement

We do not advice that you remove the pick arm for the Lexmark T644. I would suggest that you contact Lexmark Technical Support or contact a local Lexmark Service Provider (please click on the link below to locate a Lexmark Service Provider nearest to you).

Link: http://bit.ly/UeQhSB

Hi,

This link explains error 900 on a Lexmark printer. It includes troubleshooting steps in trying to resolve the issue.
http://www.marketpoint.com/article.cfm?id=100

If problem persists, contact the manufacturer.

I hope this works for you!

Thanks.

Monkey
"Understanding explains better..."

Here's an article on A 917 or 917.00 Service Error Is Appearing on a Lexmark T640, T642, T644, or an X64xe Series Printer. Just click on this link: http://bit.ly/aQD8jS. Follow the recommended actions. If error won't clear, printer may require service. Don't hesitate to contact Lexmark technical support for assistance. Thanks.

Here's an article in the Lexmark website on 80 Scheduled Maintenance" Message Appearing on a Lexmark T640, T642, T644, or an X64xe Series Printer. Included in this article are instructions on Resetting the maintenance counter to zero. Just click on this link: http://bit.ly/9pzU7R. Read thoroughly and follow the instructions carefully. Scroll down for the instructions on resetting the maintenance counter.

NOTE: RESETTING THE MAINTENANCE COUNTER SHOULD ONLY BE DONE ONLY AFTER REPLACING A NEW MAINTENANCE KIT.

Here's an article in the Lexmark website on How to Check the Paper Tray Feed Rollers on a Lexmark T640, T642, or T644 Printer. Just click on this link: http://bit.ly/b71goj. Follow the instructions carefully. Hope this helps.

Download the device-driver software from:

http://support.lexmark.com

Enter 'T640' and do a search.
Click the "downloads" tab to find the drivers (Mac? XP? Vista? Windows 7?).

There is usually no reset from the machine it is in your printer properties. Open the properties and set it to the tray you want it to feed from and usually there is a apply button try that.
Cheers
Al

This error indicates that there is a charging problem with the transfer roller. You could start by cleaning the contacts for the transfer roller (power off printer first). The transfer roller is the black foam-like roller under the toner cartridge. Handle it with paper because the oils on your hand could damage it. To remove it, just pry under the far left side with a screwdriver. Lift and pull to the left to remove. If this does not fix it, then you have a more serious problem. It could be one of the arms or the HVPS.