You don't have to read the FSX.CFG. You have to delete it, so FSX can make a fresh and new one for you restoring all the default settings.
However, if that doesn't fix anything for you, this is usually what I do if my pc is slower than expected. I am, for the record, by no means a computer expert so don't expect too much from this

:
First of all, make sure you have the latest drivers for your hardware. It could be your driver is messed up somehow and a new update will clear those faults. After installing the drivers and rebooting, check your performance.
If that didn't help, you can check how much room your hard disk has left (by going to This Computer -> *rightmouseclick on hard drive* -> Properties. It should show you a diagram of your hard disk current spare room. If the hard disk has little room left, try clearing up some space. The more free space a hard drive has, the better the performance.
Next, download CCleaner (
http://www.ccleaner.com/) which is freeware, and let it scan your computer for junk. Check if the list the program brings up really can be deleted and if so, let it delete all the junk. Now Ccleaner also has registry scan, which I personally use more than often, but several technical forums advise not to if you don't know what you are deleting. Deleting blindly everything CCleaner comes up with could end up not being able to start your Windows anymore, so be cautious.
After removing all the junk you should defragment your hard disk. And reboot after that. Check your performance again.
My last resort is a clean boot. A clean boot simply means that you deactivate all the programs and services that are not microsoft-made on boot, meaning you will start only the programs and services you would have on a fresh Windows installation. This also means for example you're antivirus probably won't be running, or your firewall (if you use a non-default one), so again, be cautious, perhaps scan your pc in advance.
I copied this from Microsoft's Help and Support (
http://support.microsoft.com/kb/310353/en-us):
To manually start Windows XP with a clean boot, follow these steps:
Step 1: Start the System Configuration Utility
- Click Start, click Run, type msconfig, and then click OK.
- The System Configuration Utility dialog box is displayed.
Step 2: Configure selective startup options
- In the System Configuration Utility dialog box, click the General tab, and then click Selective Startup.
- Click to clear the Process SYSTEM.INI File check box.
- Click to clear the Process WIN.INI File check box.
- Click to clear the Load Startup Items check box. Verify that Load System Services and Use Original BOOT.INI are checked.
- Click the Services tab.
- Click to select the Hide All Microsoft Services check box.
- Click Disable All, and then click OK.
- When you are prompted, click Restart to restart the computer.
Step 3: Log on to Windows
- If you are prompted, log on to Windows.
- When you receive the following message, click to select the Don't show this message or launch the System Configuration Utility when Windows start check box, and then click OK.
Notes
- You have used the System Configuration Utility to make changes to the way Windows starts.
- The System Configuration Utility is currently in Diagnostic or Selective Startup mode, causing this message to be displayed and the utility to run every time Windows starts.
- Choose the Normal Startup mode on the General tab to start Windows normally and undo the changes you made using the System Configuration Utility.
Step 4: Optional step to disable features
If the clean boot fixed the error, you do not have to perform this step.
Important If your problem is not fixed and you do have to follow this step, it permanently removes all restore points from your computer. The System Restore feature uses restore points to restore your computer to an earlier state. If you remove the restore points, you can no longer restore Windows to an earlier state.
This step temporarily disables Microsoft features such as Plug and Play, networking, event logging, and error reporting.
- Click Start, click Run, type msconfig, and then click OK.
The System Configuration Utility dialog box is displayed.
- Click the General tab, click to clear the Load System Services check box, and then click OK.
- When you are prompted, click Restart to restart the computer.
If these steps helped you start your computer in a clean-boot state, you are finished. If these steps did not help, go to the “Next Steps” section. If you have to return your computer to a normal startup state, go to “Steps to configure Windows to use a Normal startup state”.
Steps to configure Windows to use a Normal startup state
After you used the clean boot to resolve your problem, you can follow these steps to configure Windows XP to start normally.
- Click Start, and then click Run.
- Type msconfig, and then click OK.
The System Configuration Utility dialog box is displayed.
- Click the General tab, click Normal Startup - load all device drivers and services, and then click OK.
- When you are prompted, click Restart to restart the computer.
If that didn't work either I always get the pro's involved (close friends of mine at the university of delft =D), as I haven't a clue where to go next...