Hi, I have an iMac which I just booted up and have a white screen with a blue folder with a question mark blinking on and off. Any help would be appreciated. Tommy

Question

Hi, I have an iMac which I just booted up and have a white screen with a blue folder with a question mark blinking on and off. Any help would be appreciated. Tommy

Answer 1

That means your iMac could not find a system to use for startup.  That may mean the internal hard drive has become faulty, or the hard drive mechanism is fine, but the startup volume ("Macintosh HD" unless you renamed it) may have some type of data corruption that makes it unbootable.
First, you should try resetting PRAM
http://support.apple.com/kb/HT1379
and if that does not help, use this procedure to reset SMC (power management).  If your iMac is from 2008, this is the procedure for Intel (not PowerPC) Macs.
http://support.apple.com/kb/HT3964
(This forum category is for "iMac (PPC)," so if this iMac is older (with a PowerPC processor), please post back.)
Disconnect all peripheral devices.  When you connect it back to power, if you have been using a power strip of some type, try connecting it directly to a wall outlet, by itself (at least initially).  Start up with nothing but the power cord connected, then add only standard mouse and keyboard.  If it works, run it that way for a while. 
If PRAM and SMC reset have no effect, you should insert your Mac OS X installation disc (for the currently installed system) in the optical drive, and restart with the C key held down.  This should get you to the Installer screen, where you can run Disk Utility from the Utilities menu. 
In Disk Utility, does the internal hard drive appear in the sidebar?  If so, select Macintosh HD in the sidebar and go to the First Aid tab.  Use Repair Disk.  If an error is found, note if Disk Utility was able to fix it or not.
You can then quit Disk Utility and attempt to restart normally.