Cleaned cooling fans on hp pavilion desktop now is

This may be your bios setting also like case is removed so go to bios setting and disable the alert or you can try with fixing the ram make sure while you was cleaning you not touch to ram .may be you troche them .do 1 thing remove the ram and clean it and install it again.

It sounds like one of the fans is not spinning up after the cleaning. It's possible that the cleaning either dislodged the fan power connectors or damaged the fans themselves. Make sure that all of the fans are spinning once power is applied to the computer. Also, depending on how rigorous a cleaning it was, any other power connector or even the processor or RAM may not be seated properly. Remove power and try to gently reseat all of the RAM simms and other chips. Good luck!

Disconnect all devices from the power supply EXCEPT the motherboard
Remove any extra cards including video etc.(plug monitor into the onboard)

If you hear any beeps these can indictate where the fault is.
either of these sites below will help you further with that

Beep codes Pc

More beep codes

Power up the pc and see if the fans are working.
If not then double check the power connections to the board.

If you still have no fans it is time to suspect the power supply as the probable cause.

If the fans worked then you should have gotten a display which told you there was an error and offering you a chance to go into the BIOS. ignore it and shut down the PC.

Now connect one drive only and boot again.

Repeat that until you identify the component that is giving you a problem.

Once you find the problem then remove or disconnect and carry on with the rest to see if another component might also cause a problem

If there is only one problem device then you may want to investigate that device further, Unless you don't mind replacing it