System hangs somewhere starting windows..

Hello,

I bring my system after 6 months, its SMPS was gone . So I get new SMPS and tried to logon the system, its finely logged into windows. after second time when I tried to logged in, its hangs somewhere. Sometimes its hanged where displaying "BIOS setting" or sometimes it would hang where displaying "starting windows" message. Then Once I format my entire system and install windows 7 again. After that I could use my system without any issue(but it was too slow in operation)But nw i experience the same problem of hanging.. Please help me