Hi JayBEE, I'm sorry to hear that. If you haven't been reflashing your N900, there are few things you'd like to check first beforehand:

1) The article for reflashing your N900 is here, you'd like to read it first
2) Check the OS version of your laptop or PC. If the Windows OS version is anything other than XP, you'd like to read this section. For example, if you're using Windows 7 you'd like to download and install Windows XP Mode where you can get it free here
3) Download and install the flasher here
4) Download the ROM and eMMC image here and put them under the same directory of the flasher
5) Follow the instructions as in the link of step 2 above.

Hope this helps and wish you good luck.