If your replacing the hard-drive with an SDXC card or SSD make sure it is formatted in Fat32 otherwise the iPod will not recognize it.

My K3 had been in a drawer for 3 years. The battery was completely depleted. After leaving it on the charger for 2-3 days it was still unresponsive. I tried holding the switch in the on position for 15 seconds several times but had no luck. I eventually placed it back on the charger and held the switch in the "ON" position for 10-15 seconds and the light would illuminate amber. A few seconds after releasing the switch the led would fade out. I repeated this process 5-6 times noticing that each time the charging indicator would stay lit a little longer. Eventually it was able to power up long enough to keep charger and works perfectly now.