Mint Xfce 64-bit on sony vaio vpcy21s1e screen remains black

[marc7003]

I'm running Linux Mint "Debian" - Linux Mint Xfce 64-bit (201104)
http://www.linuxmint.com/edition.php?id=80
with all updates applied as of July 2011

It's a dual boot with Windows 7

The screen display works fine in right resolution with external screen, yet the screen display remains completey black on the laptop's 13" display, LED Backlit, 1366x768 Resolution, once grub completes start of LMDE

I assume the screen problem comes from the integrated Intel Graphics chipset
00:02.0 VGA compatible controller [0300]: Intel Corporation Core Processor Integrated Graphics Controller [8086:0046] (rev 02) (prog-if 00 [VGA controller])
Subsystem: Sony Corporation Device [104d:9076]
Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx+
Status: Cap+ 66MHz- UDF- FastB2B+ ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
Latency: 0
Interrupt: pin A routed to IRQ 42
Region 0: Memory at d0000000 (64-bit, non-prefetchable) [size=4M]
Region 2: Memory at c0000000 (64-bit, prefetchable) [size=256M]
Region 4: I/O ports at 5050 [size=8]
Expansion ROM at <unassigned> [disabled]
Capabilities: <access denied>
Kernel driver in use: i915

Btw, mouse works with external mouse not with touchpad, sound works with headphones not with loudspeakers

Anyone any idea?