Leopard starts,but when dashboard appears,screen goes black,then dasboard appears again.Death loop(

hello! seems like i've got a problem, that was not described in this forum.

what i already did:
1. installed jas 10.4.8 and created an account
2. installed leopard, which crashed at the final stage of installation. after reboot it finished the installation, but crashed with kernel panic on the first start

now i can boot up leo with -x parametr, it asks me for my password (account was made in Tiger already) and then, when desktop and dashboard appears, it throws me back to welcome screen. in was the same problem in tiger when i tryed to open "about this mac" dialog (screen goes black, and then my desktop appears again)

dear gurus solving this problem

thanks and sorry for my english