Reader Donald (who describes himself as an "old books seller"--wonder if he's describing himself or the books?) is having a problem with his system: when he rouses it from Sleep Mode (a.k.a. Standby), his browser no longer works properly.
Specifically, he says that "clicking the Firefox start link results in nothing happening. Trying to open Firefox with any of the other shortcuts has the same result. It will open only after I do a reboot."
You know the old joke about the guy who says to his doctor, "It hurts when I do this," and the doctor says, "Well, don't do that." My advice is the same: if your PC acts flaky after coming out of Sleep Mode, don't put it in Sleep Mode!
I know that's probably not the answer you were hoping for, but PCs--especially older ones--are notorious for weird post-Sleep-Mode behavior. And you said your system runs Windows XP, which means it must be a few years old at least.
Granted, there might be a BIOS update that addresses the problem, but finding and installing it can be tricky. Instead, I think you're better off using hibernate instead. I'd be willing to bet you won't encounter the problem with that mode.
Alternately, maybe it's time to start thinking about a new machine. Most of the Windows 7-powered desktops and laptops I've tested are much better at waking properly. And with nicely equipped systems readily available for as low as $400, upgrading isn't too expensive a proposition.