As explit said, reflash should fix it. In addition to that, I'll share some more or less related pieces of advice I've gathered over the years (for the times after the reflash):

• install BackupMenu and backup the phone (using a MicroSD card). I learned this the hard way and had to let go of my first N900. The USB port may become loose and then BackupMenu might be your only way to reflash.
• take a rasp tool and shave the small anchors off all of your charging microUSB cables (for the reasons above)
• if/once you have more than one battery, think about buying an external battery charger. It may prolong the USB port life as well.
• check the repositories you have on your device (especially after the reflash). Some Nokia repositories are no longer alive so you will need to replace them with community mirrors.
• try CSSU or CSSU Testing (or their Thumb versions)
• use the Faster Application Manager instead of (or in addition to) the built in App. Manager (or command line). It shows you the memory available, is much faster, searches descriptions and can also have different set of repositories than apt-get (so you can test more unstable repositories there without having to worry about breaking the system by an apt-get upgrade).
• try EasyDebian. Sometimes it is easier and safer to have newer command line tools and libraries in chroot rather than installing them on the device (where you might run out of memory or end up in dependency hell).

Good luck with your new device!

EDIT: Didn't see your above post before. Follow the steps here carefully and try different desktop operating systems for it if not successful. I don't think that a dist-upgrade would cause an absolute non-flashable brick. Also read this discussion where people had the same problem.