well...these chinese mp4s are a gamble..you'll never know whay you're getting...the other day my new mp4 charger exploded when I removed the cable...good thing the mp4 player is still ok...i'd say go for the name brands if you want a peace of mind,but if you're a risktaker like me,by all means, gimme the cheapest MP4 player available!
have you checked the battery contacts? if u have a soldering iron, you should consider re-melting the solder...that might do the trick.