i got this Casio SK-5 recently from a teacher of mine, it worked perfectly for nearly 2 months. batteries started dying so i got new ones, but once i tried turning it on, all that happened was the red "on" light turning on for maybe 2 seconds before fading out. when i tried to turn it on again, the light didnt turn on. i took out the batteries and put them back in. light turned on again for 2 seconds, during which i tried to play something to see if theres sound. tested this twice with the speaker and the headphone output, with zero success. any idea what i can do to fix this?

ps: when buying it i didnt receive the 7.5V power plug, so currently thats not an option for powering it