Hp Prime screen has interference's lines when touched with finger

[COB160]

Hi,
when I touch the screen of my Hp prime calculator in order to see calculus's history, the calculator displays horizontal lines as a interference... is it normal?

Another problem I have is that when I type this integral

https://www.dropbox.com/s/c14kw9gsmpltrb...4.GIF?dl=0

wich has simple result (displayed in the image I linked), it appears a hourglass in the place of the battery status and it happens 2 kind of things:
Either the calculator restarts displaying hp logo and a big (x^2+y^2=1) expression or the calculator does not respond any more. I am now waiting for the calculator to run out of power.

How can I fix these tho bugs? they happened since I bought the calculator.

sorry for my English