mate i had the same issue. I thought the phone was fully charged but it was not. I recommend you get a fully charged spare battery or get a desktop charger for your n900. trust me 100% its your battery. the phones firmware controls the charging. if the firmware is not there or damaged it will never fully charge, maybe only 0.1% so you might be able to turn it on for a few seconds. It keeps restarting when you try to charge because the firmware is not there or damaged. The exact same thing happened to me. I kept it on charge for 2 days and it still didn’t fully charge, when I tested my battery on another 5800 it was fully dead. I used a full battery from a 5800 and it worked for me. Trust me use another battery you know for a fact is 100% charged and try again. Thank me when it works if you go back to the start of this thread you will see that i had the same issues as you.