Sharp MX-3501N will not accept envelopes

Which model is it? The MX-350N is black and white, the MX-3501N is a color model. I'll assume it's the MX-3501N.

Either it's defaulted to print B&W in which case you just go to your printing preferences of the print driver in the printers menu in the control panel, and uncheck the "black and white print" box, or you have account/user codes that you need to enter in your print driver in order for it to print color. Instructions for adding a user code to the printer driver are found here.

Setup and Manage User Codes Account Control on Sharp Copier

http://siica.sharpusa.com/product-downloads

try this

Btw, I’m available to help over the phone in case u need at https://www.6ya.com/expert/normanj_7893313f0751935f

H3. Heat roller High temperature detection

Select the heaviest paper setting available and only use the right-side manual feed tray.

Most envelopes should work as long as you have:
1) fed them from the right side manual feed tray face down with the short side to the copier.
2) selected ENVELOPE as your paper type to run slower and lower your fuser heat.

The copier is designed for envelopes that have the flap down and the regular wettable adhesive. If you have gummed adhesive with a waxy peel strip that you remove before closing, the copier may not be designed to handle this. It may also help to put the front and rear pressure tabs on the fuser in the UP position.

Install the print driver, from the app you are printing from select your copier and then Properties, under the Paper tab you can select your paper type and tray. Only use the right side manual feed tray for envelopes. You may also need to set paper type ENVELOPE COM-10 in the copier. Extend the manual feed tray fully and set the guides or the copier will not read the correct size.

Your copier is not accepting your black toner cartridge (F2-71 Cyan, F2-72 Magenta, F2-73 Yellow). It either is not inserted properly, the packing tab is not removed from the back, or a faulty cartridge. Often 3rd party cartridges that the manunfacturer "guarantees" will work will bring this code. In short, the copier is rejecting your black toner cartridge and you should replace it.

Are you a tech or end user? This must really be done by a technician.

You really dont want to do this. It is tricky. The new belt can be pinched and ruined extremely easily, and you are required to apply it with a special lubricant. In case you really want to, The supply item is MX-4501Y1. That is just the belt. There is another kit for the transfer rollers inside. If you want to buy. $150 email me.
Remember, kit wont work without lubricant
[email protected]

bad power supply....