Why does the touchpad work in BIOS but not in Windows?

Since the touchpad works in BIOS, it is probably not completely faulty. The more likely cause is a missing or incorrect touchpad, chipset, or I2C/Serial IO driver in Windows.

Using an external mouse, try these steps:

1. Press the laptop’s touchpad function-key combination once, usually Fn plus a key showing a touchpad icon.
2. Open Settings > Bluetooth & devices > Touchpad and make sure it is enabled. If this page is missing, Windows probably is not detecting the touchpad correctly.
3. Open Device Manager and check Mice and other pointing devices, Human Interface Devices, and System devices for the touchpad, an I2C HID Device, or any device with a warning symbol.
4. Download the chipset, Serial IO/I2C, and touchpad drivers from the laptop manufacturer’s support page for your exact model. Install the chipset and Serial IO drivers first, then the touchpad driver, and restart.
5. Check Settings > Windows Update > Advanced options > Optional updates for additional driver updates.
6. If the touchpad is listed in Device Manager but still does not work, uninstall that device and restart Windows so it can be detected again.

Also check the BIOS configuration for a setting named Touchpad, Internal Pointing Device, or Trackpad and make sure it is enabled. Avoid generic driver-updater programs because the laptop manufacturer’s drivers are usually required for this type of touchpad.

A touchpad that works perfectly in BIOS but dies the moment Windows takes over is maddening, especially after you've already tried updating drivers. The good news is, your instinct is spot on—this almost certainly isn't a hardware failure. 

When you're in the BIOS, Windows isn't running, so its drivers and settings aren't in effect. Once Windows starts, it loads its own drivers for the touchpad. If the driver is missing, outdated, corrupted, or being overridden by a newer generic version from Windows Update, the touchpad can stop working.