I have a very strange problem. A few days ago Gosu just started running slow, but before it worked good! I tried to reinstall it or even whole Ruby, but it's not changing. Why it could be?

Have you recently downloaded a program? Something running in the background? If it has recently started acting up I doubt it's Gosu's fault. Something else in your computer is causing it. I have heard some comments that when an internet browser is opened, Ruby might lag some.

Impossible to tell with the given information, which operating system are you on? Which programs are running slow? etc…

I have Windows Vista, but Gosu WORKED NORMAL, even while antivirus scan. Last what I made is install ruby2exe gem. I noticed slowing after it. What to say more?

Hard to say. Does it apply to all Gosu programs? What do you use for testing it?

Can you measure the lag, is it more like one frame per second or more like just 20 instead of 60? (The former would suggest that Gosu stopped using hardware acceleration.)

-It applies to all programs.
-I'm testing it normally (like Command Prompt).
-This lag more looks like 1 FPS.
But can this hardware acceleration be stopped after reinstall?

Hmm, I know when Gosu used Direct3D a long time ago, you could check the status of HW acceleration using the dxdiag tool. I don't know if such a tool exists for OpenGL. Did you change (update) your graphics driver in the recent time?

Do you have any games that have an OpenGL rendering option (like the Quake series) that you can use to see if OpenGL acceleration works?

I'm not an expert on Windows gaming, maybe someone on the boards here knows more than me :)

I found your problem:
WINDOWS VISTA

Solution? The A+ manual says to do the following:
1. Uninstall Vista
2. Find a decently sized hammer and smash anything Vista has been applied to.
3. Continue process until it doesn't look recognizable.
4. Burn down house
5. Kill all of your relatives and friends
6. Move to Wisconsin. You're new name is "Todd Wiskhmeir". You're foreign if anyone asks.
7. Buy a Mac.

:)

8. Then realize that there is still no fixed version available for the brand new Mac OS X 10.6 and he needs to run it with a command line hack all the time. ;) That problem is almost fixed, I think, but still …

9. downgrade to 10.5 until problem is fixed ( Still better than Vista! )

I didn't updated graphic driver. It's possible that OpenGL acceleration is not working. But I don't know how to run it...