Check the enable/disable shortcut
Most laptops have an Fn key combination to toggle the touchpad (often Fn+F7 or Fn+F9). Also check if there is a physical button in the corner of the touchpad area.
Check Windows settings
Settings → Devices → Touchpad. Ensure it is toggled On. Also check "Leave touchpad on when a mouse is connected" if you use an external mouse.
Reinstall the driver
Device Manager → Mice and other pointing devices → right-click the touchpad (Synaptics, ELAN, or I2C HID) → Uninstall device → reboot. Windows reinstalls the generic driver. Then install the manufacturer-specific driver from the support site for gesture support.
BIOS enable
Some BIOS versions have an option to disable the touchpad. Check under Advanced or Main tab.
Hardware failure
If none of the above works and no driver is visible in Device Manager at all, the touchpad ribbon cable may be loose. On most laptops, this is a $5 repair — the cable reconnects under the keyboard.