As in the title: I flashed the phone a number of times but when I try to turn it on it will only show the nokia welcome screen and go blank. If I do the same while charging,it will go into a loop. I went to Nokia Care and the guy told me that he could not fix it. I am writing this post to check if he was right and I should forget about the phone and get a new one or maybe there is a way to keep my n900 alive. Please help

Well obviously the flashing didn't work correctly.

Read http://wiki.maemo.org/Updating_the_firmware thoroughly. Flash the N900 -- fully -- again, and post here the exact output of the flashing session.

Otherwise nobody will be able to know if you're doing the flashing correctly or not.