Dell Computer Won't Wake Up.

To help you in a better manner, I need a few details from you: 

1. Does the computer boot to windows?
2. Please let me know the operating system you are using?
3. Since when are you facing this issue? 

You can try the steps given below to fix the sleep mode issue, if you are able to boot to windows: 

STEP 1.

Click start
Right click the Computer Desktop ICON.  Select properties.
Press the Device Manager shield ICON.
Click Network adapters.
Double click the listed network adapter.
Select the Power Management tab.
Un-Check – Allow the computer to turn off this device to save power.

STEP 2.

Click start
Click on Computer.
Open Control Panel.
Select the All Control Panel Items option.
Select Power Options.
Click Change plan settings in the selected plan.
Click Change Advanced Power Settings.
Click the + sign next to Sleep.
Click the + sign next to Hybrid Sleep.
Select the Disable option.
Click the + sign next to Allow Wake Timers.
Select the Disable option.
Click Apply / OK. 

Please check if that fixes the issue, if the issue still persists, would recommend you to do a system restore and take the system to a prior date when it was working fine. At times it happens due to the updates not being properly installed on the system.

Click on the link below, which will list down the steps to perform System Restore: 

http://dell.to/JEe9aR 

Additionally, you can also follow some more steps as per the link below if the above steps don’t fix the issue: 

http://dell.to/NOjJjr 

You can refer the Dell Article 266452 on www.support.dell.com

Please reply if you have any further questions

Thanks & Regards
Rathish C
#iworkfordell