I have a Dell Inspiron 530S, and it exhibited the same symptoms as rguggemos's & Wilburollie's.
I can put it to sleep, but when I try to wake it, it won't. The screen will stay black. I can hear the drives spin up, and the fans go on FULL blast, and the blue power LED stays flashing, but the computer will stay like that - no picture or anything. Then I'd have to press & hold the power button to force it off, then power back on. Not ideal.
The solution that worked for me?! On boot, at the "DELL" logo, hit F2 to enter the BIOS setup, go to Power Management, and change the standby mode from S3 to S1. The difference? S3 is a "deeper" sleep, w/ more components powered off, which is better, energy-wise, but it is more difficult to wake from. S1 is a "light" sleep. Give it a shot! Maybe it'll work!
Stolen from another forum
S0 (Working) is lit. The CPU functions in entirety; the conservation of power is on a basis of by-device.
S1 (Sleep). The CPU is stopped; The RAM is regenerated; the system functions in reduced power.
S2 (Sleep 2) The CPU does not have any power; The RAM is regenerated; the system is in lower mode of the S1.
S3 (Standby) The CPU does not have any power; The RAM regenerates at minimum; the power supply unit is in mode of reduced power. This mode is also called “Save to RAM”.
S4 (Hibernate). All is powered off, but the memory was saved like temporary file on the hard drive. This mode is called “Save to disk”.
S5 (Off) Everything is shutdown. Means you need a full reboot.