My old Powerbook G4 doesn't come up

Hi. I have been using my powerbook G4 on occasion as I have all my son's photos and many memories. I was trying to copy some of the photos on a USB stick . As most of the space was taken , i could do a copy operation. I removed about 1.5 gig and tested a copy operation and it worked. today I wanted to go through the photos and copy some of them on the USB stick.

When I moved the mouse and tried to wake up the machine, it made some squeaky sounds, the screen came on and then nothing came up, every thing went black. I held the start button for few seconds and a continuous beep sound came on and then stopped. I restarted it many times but no luck. Only the CD drive disk makes a starting sound and then everything goes quiet. what could have gone wrong?

I had the USB connected to it and then removed it while these events were happening.

I have forgotten the key combination for different kinds of start up. any idea to see if my hard disk is still ok and I can recover the data?

How do I connect it to a new macbook as a hard disk? I recall I used to do that.

I have no back up of my hard disk as it is an old machine I couldn't get Time Machine to do the back up.

I am grateful for any help you can give me.

Thanks.