How can i put my uniden XS910 in standby mode????

When was the last time you checked the battery that keeps the memory alive? It's the same as your computer if it won't startup properly - it has a battery, like so many thing now-a-days

http://www.uniden.com/content/ebiz/uniden/resources/ownersmanuals/D1760om.pdf
1. With the phone in standby, press and hold # on any handset. The phone prompts you to select the number of hours (1 - 9 or Always On) that you want it to stay in silent mode.
2. To confirm, press # or just wait about 5 seconds. The phone turns on the answering system and displays Silent Mode On on each handset.
3. After the selected number of hours, the phone automatically exits silent mode. To exit silent mode manually, press and hold # again.

You may download a copy of the manual at http://www.uniden.com/content/ebiz/uniden/resources/ownersmanuals/D1680om.pdf

If the phone is in silent mode, see "Silent Mode" beginning on page 10. If the handset volume is turned down, press up-arrow while in standby mode. If the base volume is turned down, press "+" while in standby mode.

You may download a copy of the manual at http://www.uniden.com/content/ebiz/uniden/resources/ownersmanuals/DECT1480-2om.pdf.

To decrease the ringer volume, press DOWN while in standby mode.

Call waiting is a service offered by your telephone company, not a feature of any particular phone. To learn how to use it, contact your telephone company for their instructions.

On many Uniden phones while in standby mode press # then 0. If this doesn't do it, select the model of your phone from the list beginning here to download a copy of the manual.

Standby mode is when the phone isn't in the middle of a call and you're not dialing one. Simply hang up to put the phone into standby mode.

The phone is in standby mode when you're not doing anything with it. Not talking, dialing, listening to dial tone, listening to messages, going through the menu, etc.

1. With the phone in standby, press and hold # on any handset. The phone prompts you to select the number of hours (1 - 9 or Always On) that you want it to stay in silent mode.

2. To confirm, press # or just wait about 5 seconds. The phone displays Silent
Mode On on each handset.

3. After the selected number of hours, the phone automatically exits silent
mode. To exit silent mode manually, press and hold # again.

To mute the ringer, while in standby mode press the volume-down button to select Off.
To mute the microphone, while talking press the MUTE softkey.
To put the phone into do-not-disturb mode, press and hold the do not disturb button on the base.

You can download the manual from the manufacturer's web site at
http://www.uniden.com/content/ebiz/uniden/resources/ownersmanuals/TRU8885om.pdf

Standby mode is when you're not doing anything with the phone and it's just waiting for someone to call.