Hey guys. As the title says my phone isn't charging. A few months ago my phone suddenly refused to charge. The port seemed okay it wasn't shaky, like the way its been the last few times I broke it. I took it to my phone guy who told me it was a software thing. But the phone could still come on. So I got a new battery recently but it still won't charge when on. When connected to a charger when off it shows an orange light(unblinking).

Now my questions are: what's my next move? Can software really be the problem? Should I flash it? How can I tell if it's a problem with the port?

PS: I'm currently using CSSU stable, with several applications

It is most likely a flat battery.
The N900 will not charge a completely flat battery.

IRC factoid covers this best
Not all "phone guys" understand the N900 it's a different beast

I'll let you know if it works, will leave it on the charger all night. Could it be a software thing? Because when you connect it to the charger it vibrates, but sometimes the orange light doesn't come on

Easy way of curing flat battery is also old nokia dumbphone. Most of the old nokias use same or same voltage battery as the N900. You could easily use the dumbphone to charge the battery a little and so that your N900 can initialise the charging circuit. You just have to be sure that the pins are in the right order in your dumbphone battery compared to the N900 battery (+,T,-)

I used old dumbphone for a while to charge my batteries, when I had my USB broken, and still use it to charge my reserve battery. The pins were in wrong order, so I took some wires and made a cradle out of plastic and routed the wires there in right order to charge the battery easily.

Same idea as Kossuth's, only using a charger for your digital camera battery. They are also usually the same voltage and type (3.6-3.7 LiIon), but of course always check before use.

My Nokia N900 is not charging or reading charger. I think the phones are defected, as I am not the only one who has had this problem.

That sounds like a broken USB port. This is a known issue that has been discussed here a lot of times. Charge the battery with an external charger (possibly even using a method like Kossuth or I mentioned above), pop it in, boot the phone and see if the USB port works. If the phone works but the port does not, then head over here to see what your options are.