computer freezes and keyboard cannot be detected

Hmm, ok. See if this support article can help:

• If you can't connect your Magic Keyboard, Magic Mouse, or Magic Trackpad to your Mac - Apple Support

If not, I suggest that you contact Apple Support directly. Just use the "Get Support" link at the upper right-hand side of this forum's web page to get started.

See if the following support article can help:

• Connect a Bluetooth device with your Mac - Apple Support

What is the make & model of both the Bluetooth keyboard and mouse that you are trying to use with your Mac? Were you able to use them before or is this the first time use? Do you have a wired keyboard/mouse as a backup?