Check syslog, often there's either a PCI device (e.g. an ethernet card) that wakes up the machine immediately after it goes to sleep, or a process refuses to fr

Check syslog, often there's either a PCI device (e.g. an ethernet card) that wakes up the machine immediately after it goes to sleep, or a process refuses to freeze/stop. ACPI wakeup problems can be fixed using /proc/acpi/wakeup, there you'll also see which devices can wake up the machine and you can disable them one by one to find out where your problem lies (though syslog should already tell you what woke up the machine or kept it from suspending). That said I haven't had a single suspend/wakeup issue with my Linux machine in years, I even find Windows considerably more buggy and unstable in this respect.