When i switch on my dell potiplex 210l pc starts blinking orange

http://pilot.search.dell.com/dell%20210l%20service%20manual
here's your manual. has all the light codes

Normally, the amber power light means either a power supply or motherboard issue. There should also be lights on the back numbered 1-4 that give a specific error code depending on which ones are lit up. Here is a link to the manual so that you can figure out what the LED codes mean:
Dell OptiPlex 210L Quick Reference Manual Diagnostic Lights

http://search.dell.com/results.aspx?smh=sup&c=us&l=en&s=dhs&cat=sup&k=orange%20power%20light
THIS IS WHAT I CAN REFERE YOU TO.YOU DID'NT GIVE ANY DETAILS.

http://www.helpowl.com/p/Dell/OptiPlex-210L/Research/105868?search=Dell+Optiplex+210l+Beep+Codes&x=102&y=18
HOPE THIS CAN HELP YOU.

A steady or Amber blinking power button indicates a low voltage problem. This can be caused by a defective power supply or a defective motherboard. Just to make sure that nothing else is causing the problem, remove any PCI cards like modem, video card, sound card, etc... Remove the memory modules and disconnect cables to CD/DVD drives. Look at the USB ports to see if any are damaged.

The power supply is receiving power from the source but is unable to properly distribute it to the components. Either the power supply is bad or the motherboard.

Check the diagnostic LEDs and the power LED for indications of failure
Info can be found here:
http://www.fixya.com/support/r4282412-find_no_post_diagnostic_information_dell
System specific info here:
http://support.dell.com/support/edocs/systems/op210l/en/ug/tools02.htm#wp1114558

Try changing the processor and see, it really worked for me

Power supply failure
http://www.fixya.com/support/r4282412-find_no_post_diagnostic_information_dell

A faulty hardware problem.If u can check yourself then check for Ram,HDD,FDD,CDROM.Detach each and every hardware one by one.If problem persists then check for the voltage(smps),If still problem persists u have to check motherboard and processor one by one.After detecting the faulty hardware replace that with a good one.

Hope u can findout the defective spare.

Regard.

ucp_pru.