My mac takes a long time to log on, running slow

Question

my imac is running slow & takes a long time logging on, anyone knows why this happens?

Answer 1

If you have more than ten or so files or folders on your Desktop, move them, temporarily at least, somewhere else in your home folder.
Disconnect all wired peripherals except keyboard, mouse, and monitor, if applicable. Launch the usual set of applications you use when you notice the problem.
Step 1
Launch the Activity Monitor application in any of the following ways:
☞ Enter the first few letters of its name into a Spotlight search. Select it in the results (it should be at the top.)
☞ In the Finder, select Go ▹ Utilities from the menu bar, or press the key combination shift-command-U. The application is in the folder that opens.
☞ If you’re running Mac OS X 10.7 or later, open LaunchPad. Click Utilities, then Activity Monitor in the page that opens.
Select the CPU tab.
Select All Processes from the menu in the toolbar, if not already selected.
Click the heading of the % CPU column in the process table to sort the entries by CPU usage. You may have to click it twice to get the highest value at the top. What is it, and what is the process? Also post the values for % User, % System, and % Idle at the bottom of the window.
Select the System Memory tab. What values are shown in the bottom part of the window for Page outs and Swap used?
Step 2
Launch the Console application in the same way as above, and select “kernel.log” from the file list. Post the dozen or so most recent messages in the log — the text, please, not a screenshot.
If there are runs of repeated messages, post only one example of each. Do not post many repetitions of the same message.