Fluctuating fps - Vista 64bit

[LoWang]

Hello, I have a big problem because my fps is very fluctuating. For example in first level of HL2, when I stand on the platform, it changes between 1-100 approximatelly every second! It is 1600*1200 and all other settings on high, HDR, FSAA 4x and so...
the problem appears on my Vista 64bit ultimate.
CPU is Core2Quad @3.1GHz, 3GB RAM and GeForce 8800GTS 320MB (temp not higher then 80?C)
On my second system WinXP it seems to be ok. Forceware used is 169.25. In XP I have 169.21 WTH can it be? I found an old topic with the same problem, but I think this is not a network problem when I try it on single player right?
My HL2 runs in 64bit mode. Interesting thing is, that neither CSS or GMod do...
I guess I can play source games in XP, but I would really like to know what is the problem :-\

 

[AtomicSpark]

Only Half-life 2, Lost Coast, and I -think- HL2: DM have 64 bit versions. Everything else will be emulated.

 

[LoWang]

Only Half-life 2, Lost Coast, and I -think- HL2: DM have 64 bit versions. Everything else will be emulated.

and what about my fps problem? :-]

 

[LoWang]

Hey people you would not believe me, because it was so strange and hardware horribly advanced that I don't even understand it, but anyway - it is solved now
Problem was in my PCIe bus - it ran only on x1, but it should be x16. I don't know why, but manual setting of PCIe frequency to 110MHz solved the issue and it is now proper x16 (shown in CPUz / mainboard) without having to underclock my CPU back to default. Now I run my Core2Quad on 3.5GHz and the fps is quite steady