My Laptop can't handle 1920x1080, 60hz extended desktop?

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ok, i got a Toshiba A300 laptop, 2.26GHZ cpu, 4gb ram running vista64 the graphics adapter is.. ATI Mobility Radeon HD 3650 with 512mb dedicated video memory i just got a 23 inch monitor and connected to the D-sub output of the laptop. doing a 'extended desktop' thing. the 23' monitor is 1920x1080p @59hz standard. and while running the monitor, the laptop runs slightly slower, but the air come out of the exhaust vent is MUCH hotter than usual. and ATI display driver/adapter stops responding and restarts all the time... is it because that the laptop, or the graphics adapter cannot handle constant output of 1920x1080p, even the manufacturer says it's 1080p compatible but it seems that it's struggling to handle it... anyone else have the same problem? my friend has laptop with regular intel display adapter running 19' extended desktop 1440x900 and there is no problem... what do u think?