Sorry to hear your having trouble. At first blush, it sounds like it might be a battery issue. Does the Target light work? The battery connection can be a little tricky, are you happy with the connection?
How long did you charge the new battery before trying the new strobe?
Steve
Battery is in good condition. Have charged it 2 times until full.
Target light works. I can here the strobes capacitors charging when it is turned off for a while.
I have another new YS250PRO, who is working fine, but with this one the ready light is always one, no beep after recharging the capacitors.
Pfff, have had it with the 250.
I know one thing, there is no good strong flash on the market that works without problems, look at Subtronic and the last Seacam. Also more defective than working 