MOBO power plug wont go!

[RollWave]

Just got a new PSU and I cant plug in the 20pin cord from the PSU to the MOBO. FOr some reason i just cant get it to click. Is there anything I can do?

 

[RollWave]

when I plug in the power and turn it on i just hear a repeating pattern of beeps.

 

[RollWave]

one long, 2 short beeps is the pattern. Mobo is a P4C800 Deluxe (asus)

 

[lenjack]

Tell us what psu and what mobo.

 

[RollWave]

Thermaltake silent purepower 480 and ASUS P4C800 deluxe.