CPU? PSU? Motherboard?

Quick backstory:

Laptop didn't boot one day, instead made a high-pitched continuous beep when turned on. Could get laptop working by flipping it over (kind of like shaking a can of juice). Found this strange, but did this until it didn't work anymore. Looked for BIOS codes, couldn't find any on my specific BIOS (Insyde Software Brand), so kept searching for a solution. Deduced it to a hardware problem, consulted Acer, twice, and Best Buy but turned both of them down because of cost and idea that this was a simple, cheap fix. Opened up the computer, noticed my heatsink was "floating" (three of the four pylons it screwed into had come loose). Eventually found that I could screw in the pylons to reattach heatsink. Ordered screws and tried it to figure out heatsink was too tight, I think (computer wouldn't boot). Tried Gorilla Glue, and screwed the heatsink back on with small screws. Tried booting the computer, it worked on and off, and once it did work, it would blue screen and restart when tipped backwards off of its secondary cooling fan (platform underneath it). I could blue screen the thing whenever I wanted just by tipping it backwards and in odd directions.

My Problem:

How can I tell what the issue is? CPU? Power Source? Motherboard? I'm typing this to you on my computer right now. When it starts up, it's very sluggish, when it gets to windows, it's sluggish for a little while and then picks up. From time to time, my audio from the internet or from my hard drive will have intermittent lags. Imagine when you have a browser lag, and the words you type show up a few seconds after you type them, sort of like that but with audio. Same thing happens with video. The only time this doesn't occur (again this is shifty functionality here) is when a video is fully loaded, or a streaming song is fully loaded (buffered).

Acer Travelmate 4150
Pentium M 715 (1.5 GHz)(says 1.60 GHz in my computer properties)
2 GB RAM (originally 512 MB DDR2 RAM)
60 GB Hard Drive
512 DDR Memory
Reformatted from Windows XP Pro SP2 to Windows XP Pro Version 2002 SP3

The reformat was spurred on because something kept eating up all of my memory, and that still happens at when Windows first comes online. It usually tapers down to normal until I start watching videos or playing music, then something more memory intensive than the music or the video makes them lag.

ANY ideas...?