Like
Muffin_Tama has said, your Battery must have ran out.
It will beep (Like you said) to warn you it is losing power.
The average time a Tamagotchi runs out of Battery power is 4-6 months really. If it ran out eariler in that time frame someone must've gave you an used battery!
You can usually find the Batterys for Tamagotchi's at a local Convience Store, like Rite-Aid, etc.
TIPS:
Remove the Battery by taking it out of the back of your Tama with a small screwdriver.
Take the Battery out and replace it with the new one with somewhat little fingerprints on it.
Then put back cover back on your Tama.
Then after that you will see on your screen,
Download
Reset
Choosing
Reset will restart your Tama while
Download will give you your previous pet and all of his/her stats!
Good luck!
Itachi