My raspberry worked fine with a 5V-2A charger. From few days, It boots only with the energy coming from the USB cable from my computer. If I use the usual charger, it goes in a boot loop, displaying the colored screen and rebooting itself. I tried with different charger (5V-2A) and the result is the same. Why is this happening? What charger should I buy?
The Pi used to boot from a charger. The Pi no longer boots from that charger. The charger is failing, you need to buy a new one.
The Pi doesn't boot from a different charger which claims to be 5V at 2 amp. That charger is no good, you need to buy a new one.
Are you sure you haven't added something to the Pi (e.g. a new screen) which has increased the power requirements?