Excel 2007 lagging

Hi, i recently intslalled office 2007 in my old pentium 4 pc. I had problems with the excel in my 2003 version and i thought would be ok if i just reinstall office from begin,but nothing. In my excel sheets,i have problems because almost in every step i do (except writing) the excel is lagging from 2-20 sec. If im try to click undo,worse. files size are not big,700 kb around. My hard disc is ok. Printer,i checked and i set as default the one i have .
I cant see what can be the reason for these ?

***** Ι have not an English version of the 2007 office,i have a Hellenic one. In my work excel page i have 10 sheet,the first 3 they write,they dont write Sheet 1,sheet 2,Sheet 3 they write Φυλλο1,Φυλλο2,Φυλλο3 which means Sheet but in my language. The Sheets are lagging not the others who wrote the Φυλλο. I tryed to create a new workshop but i cant copy paste the comments from one to the new.

Anybody knows ?

Thanks.