I bought this for using at winter ( single house ) 3 years ago , but today it's no power up . what I should do when the info post 7 years guaranteed ?

Make sure you have a fresh tank of gas with 2 cycle oil. Also use a fuel stabilizer. Assuming you are using only 4 or 5 months a year, May need to check your spark plug since you are not using regularly and perhaps a fast start spray. I have had my Hitachi for over 4 years and never had a problem starting. Assume you are priming pump about 10 times if not used over the winter months you are gone. Warranty won’t cover neglected maintenance but this blower is worth taking to a reliable dealer of small engines if above is not working. If mechanical, then Hitachi can be contacted.