When my WinXPPro SP3 machine is in sleep/standby/suspend mode (S1 or S3), the fax modem wakes the machine some of the time but not all of the time. I want it to wake the PC every time, with 100% reliability. (When the PC is up and running, the modem and the machine receive faxes beautifully.)

What do you suggest?

Modem: Conexant D850 PCI V.92 Modem with recent driver update to version 7.67.0.50 (7/3/2007) (but this problem is the same now as before with the 2004 driver version)
PC: Dell Optiplex 755
Processor: Intel Core 2 Duo E4600 @ 2400 MHz
RAM: 2GB, of which 1.4GB is usually free
BIOS: A14
OS: WinXPPro SP3 with all updates
AV: Avast Home Free
Anti-spyware: SpywareBlaster Free, Spybot S&D Free and AdAware Anniversary Free
Fax software: MS Fax Console that comes with WinXPPro SP3
Printer/Fax Printer: HP OfficeJet Pro 8500 Wireless AIO (model A909g)
Screensaver: XP logo after 9 minutes; do NOT show welcome screen on resume
Power Settings: Home/Office Desk; Turn Off Monitor after 10 mins; Turn Off Hard Disks Never; System Standby after 20 mins; System Hibernates Never; Do NOT prompt for password when computer resumes from standby
Home network Ethernet connection: Intel(R) 82566DM-2 Gigabit Network Connection card with all Wake on LAN settings ON.
Browser: Firefox latest but use IE occasionally when necessary
Email: MS Outlook Express 6 to POP3/SMTP email service
Misc: I also run LogMeInFree version 4 on all my home computers

Thanks.

Please dont post this same question in 4 places.

Understood, and sorry for inconvenience. But I wish I knew the source of this problem.

Disable ACPI in BIOS

Mr. Stan: Thanks for your suggestion, but I'm not that knowledgeable. I know how to look for and change things in BIOS, but what is ACPI, and what bad things might happen if I disable it?

Update: I was having the very same problem with Wake on LAN as with my Wake on Ring. Since I made the original post, I've re-downloaded my chipset drivers, updated my BIOS and updated my NIC drivers via Intel PROXP.exe. For the last few days, Wake on LAN has been OK, although I see no faxes so I'm not sure about Wake on Ring. HOWEVER, now my Optiplex 755 does not seem to go into sleep/standby/suspend mode all the way. The PC power light starts blinking as it should but then comes back to a full on after a few seconds, although the monitor stays off.

Open to your further suggestions.

ACPI is a motherboard power management.
Disable it and let Windows manage the power.

Stan - How do I switch from ACPI to Windows? I see no selection option in BIOS, or in Settings ... Control Panel ... Power Options. There are quite a few references to ACPI in Device Manager, but of course without options to change.

By the way, this afternoon, my PC went back to its old tricks -- it went to sleep (with a blinking power light) but would no longer Wake on LAN or Wake on Ring. No idea why.

Thanks.

Do you have "DISABLE" option in BIOS for APCI? - Disable it!
Don't have to do anything else.
Windows will take over by itself.

There is no such option. Nothing like that at all in Power Management or anything else.