A boot-loop can have different reasons. Though in most cases this happens after flashing a new ROM, other things might affect it as well: e.g. some system related apps which have services or the like started quite early. But those special cases usually rather result in a force-close-loop than in a boot-loop.

Things you can try:

##Safe mode See whether you can boot your device into safe mode (according to an XDA post, this should be achieved by keeping Vol- and Power pressed simultaneously until the phone is booted up, and shows the string "safe mode" in the lower left corner). If that works, it is one of the apps you lately installed which causes this problem. Go and remove the app (via Settings→Apps→Manage Apps), reboot, and you should be fine. In case you get problems leaving safe mode: Power down, take out the battery for 30s, insert it again, power up.

##Recovery mode If safe mode is not reachable either, you can try booting to recovery mode (should be Vol++Vol-+Power). In the menu appearing there, select to "Wipe Cache". Reboot.

If the problem still persists, and you have no custom recovery, all that's left to you to try is a factory reset. This will wipe all your data and the apps you've installed. You can do so from the very same recovery menu by chosing "Wipe data" or "Factory reset" (it is labeled either the one or the other).

In case you have a custom recovery, you can try first to only "Wipe Dalvik Cache".

A boot-loop can have different reasons. Though in most cases this happens after flashing a new ROM, other things might affect it as well: e.g. some system related apps which have services or the like started quite early. But those special cases usually rather result in a force-close-loop than in a boot-loop.

Things you can try:

Safe mode

See whether you can boot your device into safe mode (according to an XDA post, this should be achieved by keeping Vol- and Power pressed simultaneously until the phone is booted up, and shows the string "safe mode" in the lower left corner). If that works, it is one of the apps you lately installed which causes this problem. Go and remove the app (via Settings→Apps→Manage Apps), reboot, and you should be fine. In case you get problems leaving safe mode: Power down, take out the battery for 30s, insert it again, power up.

Recovery mode

If safe mode is not reachable either, you can try booting to recovery mode (should be Vol++Vol-+Power). In the menu appearing there, select to "Wipe Cache". Reboot.

If the problem still persists, and you have no custom recovery, all that's left to you to try is a factory reset. This will wipe all your data and the apps you've installed. You can do so from the very same recovery menu by chosing "Wipe data" or "Factory reset" (it is labeled either the one or the other).

In case you have a custom recovery, you can try first to only "Wipe Dalvik Cache".