XML : buttons disappearing from a linear layout

I have a complicated linear layout, with some buttons and edittext:

          <LinearLayout          android:layout_width="fill_parent"          android:layout_height="fill_parent"          android:gravity="top|center_horizontal"          android:orientation="vertical"          android:weightSum="1"          android:layout_alignParentBottom="true"          android:layout_alignParentLeft="true"          android:layout_alignParentStart="true"          android:layout_marginBottom="400dp">            <TextView              android:layout_width="wrap_content"              android:layout_height="40dp"              android:layout_marginTop="0dp"              android:text="@string/stop"              android:textSize="18dp"              android:textStyle="bold" />                <LinearLayout              android:layout_width="wrap_content"              android:layout_height="wrap_content"              android:orientation="horizontal">          <EditText              android:id="@+id/text"              android:hint="@string/hint"              android:layout_width="match_parent"              android:layout_height="wrap_content"              android:layout_below="@+id/choose"              android:layout_alignParentLeft="true"              android:minWidth="150dp"              android:textSize="10sp"/>          <Button              android:id="@+id/text2"              android:hint="@string/favourites"              android:layout_width="match_parent"              android:layout_height="wrap_content"              android:layout_below="@+id/choose"              android:layout_alignParentRight="true"              android:layout_toRightOf="@+id/text"              android:textSize="10sp"              />              <Button                  android:id="@+id/text3"                  android:hint="@string/clean"                  android:layout_width="match_parent"                  android:layout_height="wrap_content"                  android:layout_below="@+id/choose"                  android:layout_alignParentRight="true"                  android:layout_toRightOf="@+id/text"                  android:textSize="10sp"                  />          </LinearLayout>            <Button              android:id="@+id/button"              android:text="@string/request"              android:layout_width="wrap_content"              android:layout_height="wrap_content"              android:layout_below="@+id/text2"              android:onClick="lookUp"              android:textSize="12sp"              />              <ScrollView              android:id="@+id/scrollView1"              android:layout_width="fill_parent"              android:layout_height="wrap_content"              android:background="#3d455b"              android:layout_alignParentLeft="true"              android:layout_below="@+id/button">                <HorizontalScrollView                  android:id="@+id/hscrll1"                  android:layout_width="fill_parent"                  android:layout_height="wrap_content" >                  <RelativeLayout                      android:id="@+id/RelativeLayout1"                      android:layout_width="fill_parent"                      android:layout_gravity="left"                      android:layout_height="fill_parent"                      android:orientation="vertical" >                          <TableLayout                          android:id="@+id/table_main"                          android:layout_width="fill_parent"                          android:layout_height="fill_parent"                          android:layout_centerHorizontal="false"                          android:stretchColumns="2">                      </TableLayout>                  </RelativeLayout>              </HorizontalScrollView>          </ScrollView>        </LinearLayout>    

Everything looks at it should on a large screen (tablet): I have the first line with the edittext and two buttons, on the line below I have the other button, and below it I have the scrollview (with the table). When I switch to normal screen (smartphone), only the first line is appearing, the rest not being visible. What could the solution be?