No no, the problem cannot be the phone, unless it is seriously broken (so bad it would not display anything at all)

The software to work together with flasher is within the phone boot rom.

I think you need some tweak with windows, maybe some driver or privilidge-command to make it work. In this I cannot help as I know nothing of Windoze.

Did somebody mention you need to install the nokia suite or somethong first?

Just a by the way, I had one N900 that I could not flash for more than a year with a similar error. Following the advice here, I tried it with three different operating systems on four different computers and with three different USB cables. Nothing. I put the phone in the drawer and gave up on it.

Then I upgraded my laptop and after a few months remembered about the N900. I tried it and, hey presto, it worked!

The upshot is that I can confirm, sometimes it just does not work with some computers but works with others.

I flashed my N900 again before christmas for the first time since 2013 and first time with this windows 7 PC.

I had a similar problem finding the N900 and had to install some addition driver so that Flasher could connect to the N900.

Solution
http://wiki.maemo.org/Updating_the_tablet_firmware

see the options in this section for a solution
Workaround for "no suitable device found" problem on Windows 7 x64

Try this from the general instructions:
(TIP: Hold the u key until Windows has successfully installed the driver.)

This fits perfectly. if u key is released to early and no driver is installed, windows has no clue how to handle this type of USB connection to the n900.

Else the section glo-worm mentioned has 6 suggestions.

Where this is interesting:
Once this message appears, run inf-wizard.exe from libusb-win32 package and create an inf file for "N900 (PC Suite Mode)" and install this inf driver. Then go to Device Manager and update the driver for N900 Phone Parent and the flasher should spring to life...

More instructions on inf-wizard.exe here.

But again, at this point it is definately more promising to look at Halftux footer, download the image linked in the thread, use Win32diskimager to copy it to a usb stick and boot it.

As I said before, everything is so unnecessarily complex in the windoze world

Just to check: do you open command prompt with administrator priviledges? I didn't when I first tried. I think I had to check some box from the folder options in windows to get that option to the right mouse click. Then I could open straight in windows folder the flasher with right click and open in command prompt as an administrator.

Yes, it is called "Administrator".
On systems where it exists/matters you can right click on the cmd.exe in filemanager (explorer) and select "start as administrator" which gives you something comparable to a root shell in *nixes.
The same is accomplished with the "run box" where you can type single commands from the ui.
If you enter cmd.exe in the run box and hit ctrl+shift+enter, the command is executed with admin rights.
The run box again is hidden at a rightclick on the "Start" button or in windows 10 works from the general search bar on top of the start-menü.

Geez windows is. Urrrgh, complicated indeed.

EDIT, yay maemish, we have good timing

Oh dears

use halftux image,

or
Winx64 needs definitely libusb32 (or use older XP/Win7 as 32bit)
the 'cmd' / flasher needs definitely to be run as administrator
first fix this

then 'u' needs to be hold for first time until drivers are installed
for not detecting try following sequence
take battery out
connect USB
start cmd as administrator
go to directory
start the flasher command
push (and hold) 'u'
insert battery, hold down 'u'

Pardon me for not waiting for the captain. You forgot to fly away

ica, are you able to combine what Peter listed and what you did correctly before or should i list everything in order again?

opened command promt as administrator and kept u key a good bit after getting the messagle suitable device not forund, waiting and nothing happens. also I selected that option in F8 when starting but nothing new happens. went to read halftux instructions and they are hard for me to understand guys. at this point I feel like send the n900 to the shed and forget about it