[spkguitar]

Check/change your record monitoring mode. (alt+k)

From Chapter 11 of the reference guide:

Auto Input Monitoring
In Auto Input mode, when session playback is
stopped, Pro Tools monitors audio input. When
playback is started for a punch-in, Pro Tools
monitors existing track material up until the
punch point. While punched in, the input signal
is monitored. On punch-out, monitoring
switches back to the existing track material. This
is similar to the auto-switching logic found on
digital and analog multitrack tape machines.
Pro Tools TDM systems include TrackInput
controls for setting the monitoring mode of
individual tracks. See “Selecting Record
Monitor Modes with TrackInput” on
page 149.
When using Auto Input, the switch back to
monitoring track material on punch-out is
not instantaneous.

Input Only Monitoring
In Input Only mode, when a track is record enabled,
Pro Tools monitors audio input only, regardless
of any punch-in/out selection.
When Input Only monitoring is enabled, the
Green LED next to the Transport window appear
green.

To select a record monitoring mode in Pro Tools
LE, do one of the following:

• To use Auto Input monitoring, select Operations-> Auto Input Monitor.

– or –

• To use Input Only monitoring, select Operations-> Input Only Monitor.

To toggle between Auto Input and Input
Only monitoring, press Alt+K (Windows)
or Option+K (Macintosh).